[0001] The present invention concerns a method for controlling bacterial infection in the
sugar production process. More specifically, the invention concerns a method for controlling
bacterial infection of raw sugar solutions obtained from sacchariferous material of
vegetable origin, and particularly from sacchariferous plants such as sugar beet or
sugar cane, based on the combined use - according to specific procedures - of two
different kinds of agents having antimicrobial and/or bacteriostatic activity, both
suitable for being employed in the processing of food products destined for human
or animal consumption.
[0002] As is known, in the production of sucrose or other sugar products based on raw vegetable
material, primarily sugar beet and sugar cane, the vegetable material is first disintegrated
mechanically and then undergoes extraction, or pressing, in order to obtain the raw
sugar solutions from which, via subsequent operations, purified sugar in a solid state
is obtained. Since they are agricultural raw materials, it is inevitable for the raw
vegetable products to contain micro-organisms such as bacteria, yeasts or moulds,
most of which are eliminated via initial washing. Those that remain, attached to soil
particles which are not removed through washing, can easily develop within the processing
system since the treated raw sugar solutions can act as nutrients for these organisms.
[0003] Considering, for instance, the sugar beet production process (from Beta vulgaris),
after the beet - with leaves removed - is washed and sliced, it is scalded in order
to break down - by denaturation - the cells containing the dissolved sugar. In fact,
slicing the beet only partly leads to breaking down the cell membranes, while the
remaining cells remain intact. In order to obtain the sugary juice by extraction,
the slices (cossettes) must undergo heat treatment in order to denaturate the cell
membranes. This treatment should take place at the highest temperature possible (such
as 80°C) for a few minutes. Then, the cossettes undergo an extraction process by diffusion,
normally carried out in counterflow continuous cycle devices (diffusers), in which
the sucrose is transferred into an aqueous phase called raw juice or diffusion juice.
The residual solid phase of this operation is composed of the so-called spent pulps
or spent cossettes. The extraction by diffusion section is fed, in counterflow, by
an aqueous extraction medium partly consisting of fresh water and partly recycled
water coming from the pressing of the spent pulps. Further micro-organisms can thus
be introduced into the system through the extraction water.
[0004] In view of the above, it is evident that the diffusers of a sugar beet extraction
system are excellent incubators that can multiply the bacterial population, and that
the contact time inside them influences bacterial growth, while the working temperature
exerts a selective action on the species that prosper. In fact, the temperature inside
the extraction system influences the vital functions of the micro-organisms and, while
low temperatures (< 40°C) tend to facilitate the growth of mesophilic bacteria, and
particularly lactobacilli, high temperatures tend to promote thermophilic bacteria,
such as
Bacillus stearotermophilus and
Clostridium thermosaccharolacticum, in particular. Both kinds of bacteria degrade the sugars contained in the treated
raw sugar material, mainly giving rise to the forming of lactic acid and other products
of their metabolism, such as lower fatty acids (acetic, propionic and butyric acids),
ethanol, acetone and gaseous products such as NO
2. This obviously leads to sugar loss in the finished product and, in serious cases
of infection can have economically serious consequences.
[0005] Moreover, the micro-organisms that are present cause an enzymatic splitting of the
sucrose molecule, with the production of the two constituent monosaccharides - glucose
and fructose (D(+)-glucose or dextrose, and D(-)-fructose or levulose). The hydrolised
product thus obtained, which is made up of two reducing sugars whose aqueous solutions
have an overall optic power opposite to that of the initial sucrose solutions (dextro-rotatory),
is called "inverted sugar". The presence of inverted sugars in the diffusion juice,
besides accompanying a loss in sugar, also gives the juice a darker colour and thus
needs greater processing and further sugar losses for the final washing.
[0006] The intensity of bacterial activity varies during the sugar production campaign,
which is subject to considerable climatic changes that produce effects on the quality
and on the state of cleanliness of the beet delivered to factories. The more deteriorated
and dirty the beet, the greater the virulence of microbiological activity within the
extraction systems. Slowdowns in production, due to a lack of beet supply or mechanical
breakdowns, can have the same effect since they increase residence times and lower
the temperature. Moreover, as noted, the direct economic damage caused by sucrose
destruction is accompanied by the indirect damage caused by the effects that the products
of microbiological activity have on the process. The lactic acid destroys the natural
alkalinity of the juices, while the reducing sugars increase their colouring.
[0007] The proliferation of mesophilic bacteria can be reduced by avoiding, as much as possible,
long stays, temperatures lower that 40-50°C and production system stoppages, and is
in any case avoided with the exposure to high temperatures. However, for the deactivaton
of thermophilic species and for controlling infections due to these micro-organisms
it is necessary to have regular treatment with suitable disinfectants. The sugar industry
is aware of the potentiality of problems linked to bacterial proliferation and has
long been using various bactericides. The most widely used of these is formaldehyde,
followed by dithiocarbamate, glutaric aldehyde and quaternary ammonium salts.
[0008] In particular, formaldehyde or formalin is used in 30-40% solutions, such as by adding
it in considerable quantities for a very short time (an intermittent, shock, dosage)
in one or more stages of the system, such as in quantities of 0.5-1.0% of the hourly
flow rate of the raw juice (that is, 50-100 kg of formaldehyde per 100 m
3 of treated raw juice per hour). The intervals between one shock dose and another
can vary depending on the intensity of the infection, but on average there is one
treatment every 8-24 hours (1-3 shocks per day). The effects of antibacterial treatment
are normally monitored, by determining the lactic acid concentrations in the extraction
system.
[0009] Although its antimicrobial effectiveness is well-known, the addition of formaldehyde
to the raw sugar juices has the disadvantage of worsening the colouring of the juices,
thereby increasing the sugar washing cycle - and thus the process time as a whole
- as well as the sugar loss.
[0010] Moreover, and more critically, for formaldehyde there are normative restrictions
for environmental reasons, given its evident carcinogenicity. Also the other aforesaid
biocides are not devoid of possible negative effects when destined for uses linked
to foodstuffs. It must be noted, in particular, that the spent beet pulps, which are
traditionally destined for animal feeds, have recently been included, by the effects
of legislation, in the category of products for human consumption. The greater attention
that government and health organisations at European and world level are devoting
to food safety places a serious possibility on the use of these biocides and justifies
the current need for new systems for controlling bacterial infections that take these
limitations into account.
[0011] One class of disinfectant compounds that were proposed and have been used for some
time for controlling bacterial infections in the food industry - and which do not
involve the aforesaid safety risks - is composed of peroxycarboxyl acids, and specifically
of peracetic acid or peroxyacetic acid (PAA, with the formula CH
3-CO-OOH). Mixtures of peracetic acid and hydrogen peroxide (or oxygenated water, H
2O
2) in various molar ratios have been used as disinfectants in the sugar industry, in
the implementation of methods involving additions of product at various dosages and
different H
2O
2/PAA ratios, at different stages of the production process.
[0012] Specifically,
European patent EP 0678123 (Solvay Interox) describes a process for the disinfection of raw sugar juices in
which a solution of peracetic acid with a H
2O
2/PAA molar ratio of at least 12:1 is fed into the pulp pressing water system and a
solution of peracetic with a H
2O
2/PAA molar ratio lower than 10:1 is fed into an intermediate point of the diffusers.
The bactericide solutions, which are marketed under the Proxitane
® trademark, are preferably dosed: one in a continuous manner (such as at a concentration
between 2 and 3% weight of PAA and 20-30% weight of hydrogen peroxide) in the press
water system (in particular, so as to obtain PAA concentrations in the treated waters
in the region of 5-50 ppm), and the other in the form of shocks in the diffusers (preferably
in concentrations of 25-350 ppm of PAA, for example, with a shock concentration of
210 ppm, subsequently maintained at an average level of 130 ppm by a 10-minute dose
every three hours).
[0013] Other technological proposals, still based on the use of disinfectant solutions based
on peracetic acid and hydrogen peroxide, are described, in particular, in
European patent EP 0943692 (S.E.P.P.I.C.) and in
European patent EP 1138787 (S.E.P.P.I.C. and Bioxal). The former essentially proposes using a single formulation
of peracetic acid solution with a H
2O
2/PAA molar ratio not above 4, introducing the solution in at least one stage of the
system upstream of the diffusers and in at least one stage of the pulp press water
system. The second document instead proposes a more complex scheme, which involves
dosing the peracetic acid/hydrogen peroxide solution, in various concentrations but
still with the same ratio between the two components, onto the beets before slicing
them, onto the already cut cossettes, in at least one stage of the system upstream
of the diffusers and in at least one stage of the pulp press water system, as well
as continuously in the recycled diffusion water system.
[0014] It must be noted that peracetic acid, besides having a disinfectant action, presents
some positive side effects on the sugar production process that no other type of bactericide
can produce. Among these it is possible to cite the following.
- a) A positive effect on the pressability of the spent pulps. With equal diffusion
operating conditions and equal doses of press coadjuvants (typically calcium sulphate
and aluminium sulphate), the presses produce pressed pulps with a greater content
of dry matter and less water content. This benefit can be exploited in order to reduce
press coadjuvant consumption, increase the diffusion temperature or reduce fuel consumption
in pulp drying.
- b) An effect on the colour of the depurated juices: treating the diffusion juices
with PAA leads to a reduction of the colour of the depurated juices, due both to direct
action on chromophor groups, and indirectly because formalin use is avoided (formalin,
as is known, has a colouring effect on the juices). Reducing juice colouring means
greater value of the sugar produced or reducing the costs of refining white sugar.
- c) An effect, found during the studies carried out within the present invention, of
reducing inverted sugar content. It was found that using PAA produces a drastic abatement
of glucose and fructose in the raw diffusion juice, presumably because of inhibition
of the enzymes dealing with converting the sucrose into the two simple sugars. This
benefit, besides involving a reduction in sucrose loss, also reduces the negative
effects of inverted sugars on juice colouring and on the content of the calcium salts
soluble in the depurated juice.
- d) A positive effect, as has been found within the studies connected to the present
invention, on the content of calcium salts in the purified salts. The observed effect
may be attributed both to the reduction in the sulphates introduced as press coadjuvants
and to the reduced contribution to the forming of organic acids, in the depuration
phase, due to the presence of glucose and fructose.
[0015] Despite the advantageous effects found in using peracetic acid as a disinfectant
for the raw sugar juices produced in industrial sugar production (as is also demonstrated
by the fact that different alternative methods of treatment have been proposed over
the years in the sector, all consisting of application variations making use of the
same biocide agent), any disinfectant method using only peracetic acid, however dosed
and distributed inside the system, cannot guarantee total protection from bacterial
infections that can arise during the sugar production process. The PAA and hydrogen
peroxide mixtures, in fact, are in any case subject to gradual loss of efficacy due
to the onset of resistance phenomena. It is known that all micro-organisms, when subjected
to repeated applications of the same antibacterial agent, can - in time - develop
insensitivity to the specific agent, owing to the natural selection of strains resistant
to the agent concerned.
[0016] Moreover, it has been found that PAA use poses further limitations when, in order
to contrast bacterial resistance phenomena, it is decided to use higher doses of the
same agent, or to suspend it in order to use another chemically different bacterial
agent. In fact, the increase in the presses efficiency in terms of dry matter content,
and thus of energy consumption for the subsequent drying stage (which is one of the
effects of using peracetic acid as a disinfectant for raw sugar juices), subjects
the presses to greater torsional stress which, if not controlled, may seriously damage
them.
[0017] Both lactic acid, produced by bacterial activity, and PAA act as pressing coadjuvants.
In a system under control, the combined effect of lactic acid and PAA used as a moderator
of bacterial activity, and thus of the lactic acid level, enables controlling the
presses stress simply by reducing the use of calcium sulphate and aluminium sulphate
(which, as is known, are commonly used as coadjuvants to increase press yields). When
infections go out of control and the lactic acid concentration sharply rises, causing
an increase in the presses stress, it may become impossible to use PAA as an antibacterial
agent so as not to accentuate the risk of damaging the presses themselves. In this
stalemate situation, it is necessary to suspend the PAA treatment and use an alternative
antibacterial agent. However, suspending PAA and using an alternative method causes
a decompensation in carrying out the process, due to the fluctuation of those parameters
influenced by PAA (pressability, colour, glucose and calcium salts in the juices).
[0018] In view of the above, the present invention thus aims at providing a method for controlling
bacterial infection in processes for the production of sugar from vegetable materials,
and particularly sugar beet and sugar cane - the method making use of disinfectant
products compatible with the food industry and devoid of any negative effects for
their use in both human and animal foodstuffs, but at the same time able to effectively
combat the bacterial infections that can arise during the sugar production process,
reducing as much as possible the loss of product and all the other inconveniences
that result from the said bacterial infections. The process studied according to the
present invention is based on improving the performance of the peracetic acid/hydrogen
peroxide system and overcoming its limitations of use, in order to exploit, without
any fluctuations disturbing the conductance of the extraction process, the technological
benefits brought by this system and avoiding the onset of critical conditions to the
presses, due to the loss of control over lactic acid production.
[0019] To this end, the present invention proposes the joint, but not alternative, use of
a second type of bactericide - also having compatible characteristics for use in foodstuffs
- consisting of natural plant extracts such as those obtained from hops, wood and
the exudates of conifers, or from palm kernels.
[0020] The antimicrobial properties, or in any case bacteriostatic ones, of certain natural
plant extracts such as hop extract or resin extracts like rosin or other natural resins,
have been known since ancient times, but only recently have these products been proposed
as antimicrobial agents in the sugar industry. Specifically,
European patent EP 0681029 (Zuckerforschung Tulln) describes the use of hop extracts as inhibitors of bacteria
proliferation (thermophilus bacteria) in sugar extraction processes using an aqueous
medium, wherein these extracts, or their components, are dosed - either continuously
or as shocks - in raw sugar juices, to work at temperatures ranging between 50°C and
80°C. More specifically, the description illustrates the use of hop extracts as they
are (whose bacteriostatic properties are already well known and used in beer production)
or their active constituents, the so-called beta-acids or "lupulons" and the so-called
alpha-acids or "humulons", contained in hops, either in a dissolved or emulsion form
in the aqueous medium. These agents, of which a commercial version is available under
the BetaStab
® (BetaTec) trademark, are considered very active against the types of bacteria found
in raw sugar juices during sugar production processes. However, also in this case
their continual use for a certain period of time may lead to the onset of resistant
bacteria strains.
[0021] Similarly, and in order to broaden the range of natural products that can be used
as antimicrobials in the sugar industry,
US patent no. 6770147 (Zuckerforschung Tulln) proposes formulations based on natural resins compatible
with foodstuffs, and preferably resin acid extracts obtained from conifers, either
substituting or in addition to hop extracts, to be used when treatment with the former
gives rise to resistance. As is known, conifer resin extracts (rosin or colophony)
are composed of various diterpenes, amongst which the most important are abietic acid,
neoabietic acid, palustric acid and levopimaric acid, and they have a natural antibacterial
activity.
[0022] Also within the same range of natural antibacterial products of vegetable origin,
the extracts of the palm kernel (or palm seed oil) of an African palm from which palm
oil is traditionally obtained have recently been proposed. The fatty acids of palm
kernel, amongst which there is firstly myristic acid (linear aliphatic carboxy acid
of 14 carbon atoms), but also, for example, lauric acid (dodecanoic) and palmitic
acid (hexadecanoic), also have a marked antibacterial activity and can be used as
natural agents for controlling bacterial infections in raw sugar juices of the sugar
industry.
[0023] According to the present invention, it has been found that the continuous application
regimen of the PAA-based disinfectant system may be advantageously integrated, in
order to eliminate episodes of resistance to this antibacterial treatment, with a
simultaneous treatment for short periods with an antibacterial agent made up of natural
plant extracts of the kind just mentioned, which will be cumulatively indicated as
NVE (natural vegetable extract), regardless of the specific chemical constitution.
[0024] The efficacy of the coordinated use of NVE was experimented, according to the present
invention, along with the constant use of a powerful oxidant as peracetic acid/hydrogen
peroxide, from which there was expected a marked inhibiting action on organic matrix
agents (as is, indeed, a natural vegetable extract). On the contrary, according to
the present invention, it was found that the second agent, operating in an environment
made absolutely devoid of species resistant to this second agent - thanks to the continuative
use of PAA - has a considerable effect able to rapidly eliminate PAA-resistant species.
In practice, the combined use of the two agents, instead of giving rise to interferences,
leads to a synergic effect, enhancing the efficacy of both agents concerned.
[0025] Thus, the present invention specifically provides a method for controlling bacterial
infection in the sugar production process starting from sacchariferous vegetable materials,
wherein to sugary material to be treated there is added one or more solutions based
on peracetic acid and hydrogen peroxide, as a primary disinfectant, at least one of
which is fed to the process in a continuative way, characterised by the fact that
a further product is also added as a secondary disinfectant, and namely a product
based on natural vegetable extracts compatible with foodstuffs and having antibacterial
activity.
[0026] For the purposes of the present description, the term "continuative" is generally
taken to mean the use of a disinfectant agent that may consist of the continuous feeding
of the said agent, without interruptions, into one or more stages of the sugar production
process, or of discontinuous feeding, at intervals, but which is nonetheless on a
regular basis over time and with no interruptions. The "continuative" use of the PAA/H
2O
2-based disinfectant may advantageously consist of, for example, a continuous feed
in one stage of the extraction system, accompanied by "shock"-based feeding at regular
intervals in another stage of the system, on condition that at least one of these
two feeds does not incur interruptions for the entire duration of the treatment session
considered.
[0027] Still for the purposes of the present description, the term "non-continuative" is
taken to mean the use of the disinfectant agent in a sporadic or episodic manner for
a limited and circumscribed period of time with respect to the overall duration of
the treatment session considered (and specifically, a sugar production campaign).
Within the periods of use, the disinfectant used in a "non-continuative" manner may
be fed into the process both with a continuous flow or with shocks at regular intervals.
[0028] Furthermore, for the purposes of the present description, by "antibacterial activity"
is meant to be an actual bactericide activity or also a merely bacteriostatic activity,
that is, such to inhibit the growth and proliferation of bacterial micro-organisms
without necessarily causing their death.
[0029] Preferably, according to the present invention, the NVE-based product is selected
from the group consisting of: hop extract or one or more of its constituents having
antibacterial activity; vegetable resins compatible with food consumption or one or
more of their constituents having antibacterial activity; palm kernel extracts or
one or more of their constituents having antibacterial activity; or a mixture of two
or more of the said products. In particular, the NVE-based product is preferably composed
of hop extract, or of a mixture of hop beta-acids, or of a mixture of hop alpha-acids.
[0030] According to some embodiments of the proposed procedure, the said NVE-based product
is a moderately alkaline aqueous emulsion containing 5-20% by weight of acids or other
natural compounds having antibacterial activity. In the case that the NVE-based product
is based on hop extract, it will contain, preferably, 80-90% by weight of water, 1-3%
by weight of potassium hydroxide, 8-12% by weight of beta-acid, and 1-5% by weight
of other hop compounds.
[0031] The method for controlling bacterial infection proposed according to the present
invention, when applied to sugar beet production processes, preferably involves an
application scheme in which, of the said one or more PAA-based solutions, a first
solution is continuously added in the press water system (that is, in the juice obtained
from pressing the pulp and which is wholly recycled in the diffusers) and a second
solution is added in the form of shocks, in one or more of the following stages of
the production process: inside the diffusers, in the extraction juice system, in the
juice-cossette mixer, in the juice-cossette line, according to where infection areas
are located, monitored by analysing parameters indicating the intensity of microbiological
activity.
[0032] These solutions based on peracetic acid and hydrogen peroxide preferably contain
- similarly to the commercially available solutions of the prior art - 2-15% by weight
of peroxyacetic acid and 15-50% by weight of hydrogen peroxide, and may also contain
5-25% by weight of residual non-reacted acetic acid as well as 0.5-1.5% by weight
of other acids used as stabilisers in the peracetic acid manufacturing process.
[0033] The first peracetic acid-based solution continuously added in the press water system
is preferably fed at a dosage ranging between 0.1 and 30 ppm of peracetic acid, preferably
in the dosage range of 0.3-10 ppm of peracetic acid, while the second peracetic acid-based
solution is preferably added in the form of shocks with an average dosage ranging
between 3 and 120 ppm of peracetic acid, preferably between 3 and 60 ppm and with
a frequency ranging between 3 and 12 times a day.
[0034] During continuative use of PAA, the disinfectant process provided by the present
invention envisages the timely and/or preventive check for the onset of PAA-resistant
species. At the same time, to avoid the secondary bactericide agent - and namely NVE
- from causing the development of resistant species, this must be used for short periods
and at intervals not too close to one another.
[0035] According to certain specific embodiments of the proposed method, the NVE-based product
compatible with foodstuffs and having antibacterial activity used in a non-continuative
manner is fed into the process on the onset of species resistant to the peracetic
acid-based disinfectant. In this case the NVE-based product is preferably fed in the
form of shocks with a frequency ranging between 1 and 6 times a day and in dosages
between 5 and 50 kg of product per shock, until such time as a pre-established level
of reduction in bacterial activity is ascertained. In these conditions, which correspond
to the most critical situations, it is worth having recourse to a timely check, that
is calibrated in dosage and frequency of the shocks, according to the bacterial activity
ascertained.
[0036] According to other specific embodiments of the proposed method, which are generally
applicable to a fully operational production plant and with beet of good quality,
the NVE-based product compatible with foodstuffs and having an antibacterial activity
is fed into the process - for preventive purposes - at pre-established time intervals.
In this case the NVE-based product is preferably fed in as shocks with a frequency
of between 1 and 3 times a day and in doses ranging between 5 and 20 kg of product
per shock, one day a week.
[0037] In each of the two cases mentioned, however, the frequency of the shocks and the
dosages depend on the operating conditions and on the state of the beet concerned.
[0038] In intermediate conditions in terms of type of control, the dosage and frequency
of shocks must be determined according to the parameters indicating the intensity
of the microbiological activity.
[0039] Also the secondary disinfectant based on NVE can be fed into the process at one or
more (such as by rotation) of the following stages of the production process: inside
the diffusers, in the extraction juice system, in the juice-cossette mixer, and in
the juice-cossette line.
[0040] The specific characteristics of the present invention, as well as its advantages
and relative operative procedures, will be more evident with reference to the detailed
description presented merely for exemplificative purposes below, along with the results
of the experimentation carried out on it and the comparative data with respect to
the prior art. The present invention is also illustrated in the attached drawings,
wherein:
Figure 1 shows a table graphically summarising the field trials carried out in order
to assess the method according to the present invention during a sugar production
campaign, with the indication of the various agents used and the treatment duration.
Figure 2 shows the trend of the L-lactate values, in g/I, assessed in the beet cossettes
fed to the process and in the average raw juice, determined during the field trials
summarised in Figure 1.
Figure 3 shows the trend of the glucose values, in g/I, assessed in the beet cossettes
fed to the process and in the average raw juice, determined during the field trials
summarised in Figure 1.
Figure 4 shows the trend of the concentration of calcium salts, expressed as hardness
in French degrees, in the clear liquid of 2nd saturation and in the thin juice, determined during the field trials summarised in
Figure 1.
EXAMPLE 1
[0041] The experimentation had an overall duration of about 51 days and took place in three
separate periods preceded by a conventional formalin treatment and alternating with
a trial with vegetable extracts having disinfectant activity (NVE - hops). The diagram
shown in Figure 1, herewith attached, graphically summarises the periods concerned
and the operation trend.
[0042] Period using formalin: from the beginning of the campaign until 25 August, carried out at an average dosage
of 390 ppm. Moreover, about 75 t of aluminium sulphate and a little under 276 t of
CaSO
4 was also used. The lactic acid stayed at an average level of 270 ppm.
[0043] Period using PAA no. 1: this started on 26 August and lasted 17 days. Not having yet acquired the handling
competence necessary to manage the lactic acid levels, on the one hand, and the absorptions
of the presses, on the other, it became necessary to use formalin often at higher
doses than necessary in order to maintain control of the press absorptions. That is
why there was an accentuated variability in the lactic acid values, with repercussions
on the colour and calcium salt values.
[0044] The use of aluminium sulphate was completely suspended throughout the period and
the use of chalk was reduced.
[0045] Period using NVE-hops: this started on 12 September and lasted about 10 days. In the first part, thanks
to the quick pace and absence of resistant species, the efficacy appeared very satisfactory.
In the second part, instead, also following a slowing down in pace, it became necessary
to use formalin.
[0046] In this period, the disappearance of the technological benefits linked to colour,
to glucose in the juices and to the pulp pressability was observed, so much so that
it became necessary to resume use of aluminium sulphate and to go back to the habitual
dosages of calcium sulphate.
[0047] Period using PAA no. 2: this started on 22 September and lasted for 17 days until there was a halt on 8 October
for lack of beet supply. The experience gained, during most of the period in which
the operating pace was characterised by a constant quick pace, enabled maintaining
both the control of the lactic acid levels and the press absorptions, without the
need to resort to the second biocide.
[0048] The second half of the period saw the employment, by implementing the procedure according
to the present invention, of targeted shocks of the second bactericide, and namely
consisting of NVE-hops (natural vegetable extracts from hops).
[0049] In none of the occasions above was use made of aluminium sulphate, while calcium
sulphate was reduced to about 1/3.
[0050] This period was selected as significant for comparison with the formalin period,
thanks to the acquired management regularity.
[0051] Period using PAA no. 3: this started on 13 October, straight after the pause for lack of beet, and ended
on 24 October in order to run down formalin stocks.
[0052] The period was characterised by very low and inconsistent operating paces which made
it necessary, from time to time, to make use of a second biocide, and namely formalin
(as noted, in order to run down stocks)
[0053] Table 1 below reports the dosages of the disinfectants and press coadjuvants used
in the various periods.
TABLE 1
Sugar production campaign - Periods |
|
|
Formaldehyde |
PAA 1 |
Hops |
PPA 2 |
|
PAA 3 |
|
Cut beet |
t |
264,014 |
184,340 |
95,119 |
156,518 |
|
89,341 |
Formaldehyde |
g/t |
348 |
74 |
73 |
4 |
|
34 |
Hops |
g/t |
- |
- |
21 |
6 |
|
0 |
PAA 3% |
g/t |
- |
39 |
- |
56 |
|
50 |
PAA 12% |
g/t |
- |
76 |
- |
63 |
|
63 |
Al(SO4)2 |
g/t |
457 |
- |
- |
- |
|
- |
Ca(SO4)2 |
g/t |
1,292 |
413 |
- |
- |
|
- |
Operating conditions
[0054] The PAA/H
2O
2 application model was adopted, which refers to patent
EP 0943692, based on the following operating procedures:
■ PAA in continuous dosage on the press water; namely, a 3% solution was used.
■ PAA dosed in shocks inside the diffusers and in the mixers/scalders; namely, a 12%
solution was used.
[0055] In sum, an average dosage of about 50 ppm of 3% solution on the press water and of
about 70 ppm, on average, of 12% solution in the diffusers was recorded.
[0056] The handling, stockage and distribution of solutions containing PAA is a critical
factor. That is why particular care must be taken in adopting measures and provisions
geared to assuring the maximum safety standard possible.
[0057] As regards the 3% solution, the dosage was carried out in continuous mode by means
of a dosage pump, directly on the press water tank upstream of the depulping filters.
[0058] The 12% solution was dosed by means of electrovalves activated from the control room,
mainly at 1/3 of the height of the towers and to a lesser extent in the mixer, in
the juice-cossettes line and on the grill washing juice.
Conclusions
[0059] It was possible to see that the second bactericide, applied as a support to PAA with
primary bactericide functions, had a greater than expected efficacy, finding itself
operating in an environment devoid of resistant species. This behaviour turned out
to be extremely useful for controlling the critical situations that arise, for example,
during operation at a slower pace.
[0060] For its part, the PAA applied regularly as a primary bactericide confirmed the expected
technological benefits relative to:
- Pulp pressability
- Juice colour
but also had a significant impact on the following parameters:
- Reduction of the inverted sugars
- Reduction of calcium salts
[0061] It may thus be concluded that the continuative use of PAA, besides having the known
disinfectant action, produces a series of technological benefits of high economic
return, while the use of a second bactericide, applied in an environment characterised
by the development of PAA-resistant species, but extremely sensitive to different
molecules, appears extremely effective in supporting the basic control function entrusted
to PAA.
[0062] The combination of PAA with NVE, and namely hop extracts, but also resin extracts
of conifers or palm kernel extracts, or one or more of the respective constituents
having antibacterial activity, meet the food safety standards required for all those
products to be applied in direct contact with human foodstuffs or assimilated as such
(spent pulps).
ANALYSIS OF THE RESULTS
Control of infections
[0063] The control of the infections was conditioned by the pace of the diffusions and by
the press absorptions.
[0064] The low temperature conditions and high retention times that come about during reduced
operating paces make it difficult to control the infections. Moreover, during the
experimentation with PAA, it became necessary to face an additional critical factor:
press absorptions.
[0065] As is known, the PAA used in order to control lactic acid levels and the pH of the
juices also exerts a strong influence on the solid matter of the pulps and on the
absorption of the presses: this condition, especially in the first trial period, led
to using occasional formalin shock treatments for fear of damaging the presses.
[0066] In the second period of PAA use, half characterised by a regular quick operating
pace, it was not necessary to use the second disinfectant proposed according to the
present invention. With a reduced operating pace - a situation that arose in the second
half of the period concerned - use was made of 1-2 shocks a day of NVE from hops as
a support biocide.
[0067] The attached Figure 2 reports the lactic acid levels in the average raw juice throughout
the period under study, with respect to the one contributed by the beet cossettes.
[0068] In sum, it was possible to observe that the second biocide, used in the absence of
resistant species, turned out to be very effective.
Impact on inverted sugars
[0069] During the experimentation it was possible to observe an interesting behaviour of
glucose in the diffusion juices, and this is well illustrated in the graph of the
herewith attached Figure 3.
[0070] In the first month of the sugar production campaign, coinciding with the use of formalin,
there was an increase of glucose, equal to 380 ppm, with respect to the one coming
from beet. A similar behaviour was found during the 10 days of hop treatment. For
the rest of the campaign characterised by PAA use, except for the week run with hop
NVE, the trend decreased until it finally annulled itself completely. In other words,
with PAA treatment the excess glucose disappears, with modest increases of lactic
acid levels (from 0 to a maximum of 80 ppm).
[0071] Finally, it was observed that the drastic reduction in inverted sugar in the diffusion
juice was accompanied by:
■ A reduction of the colour of the thin and dense juices by about 1000 UI.
■ A reduction of calcium salts in the clear juice of 2nd saturation and in the thin juice by about 10°F.
■ A reduction of glucose in the dense juice.
[0072] Since the above-described phenomenon appears interesting both from a technological
and economic standpoint (a reduction of losses), an attempt was made to explain the
reason for this.
[0074] The above-described phenomena, either singly or in combination, could explain the
presence of newly formed glucose during the use of formalin and hops.
[0075] Vice-versa, to explain its disappearance when PAA is used, the most likely hypothesis
is that no additional inverted sugar is formed, thanks to a possible inhibiting action
by PAA on the invertase and/or to the lack of destructive action on bacterial membranes
on the part of the PAA, to which would correspond the lack of release of new enzymes
in the diffusion juice.
Impact on the calcium salts in the depurated juices
[0076] The graph of herewith attached Figure 4 shows the trend of the calcium salts in the
clear liquid of 2
nd saturation and in the thin juice. There is a significant decrease in calcium salts
from the time PAA starts to be used and up to the end of the campaign, with the exception
of the hop period, which resumes the trend found with formalin.
[0077] The variation is seen with a "step" right at the point where there is the shift from
formalin to PAA on 26 August, despite some formalin shock due to inexperience.
[0078] Table 2 below reports the averages in hardness, relative to the two juices, for each
of the periods the experimentation was divided into.
TABLE 2
|
Hardness °F |
|
Formalin |
PAA 1 |
Hop |
PAA 2 |
|
PAA 3 |
Δ |
Thin |
19.26 |
11.19 |
12.02 |
11.05 |
|
11.35 |
8.20 |
2nd carb. |
44.42 |
38.80 |
36.87 |
32.79 |
|
27.47 |
11.63 |
Δ2nd carb./Thin |
25.17 |
27.62 |
28.85 |
21.73 |
|
16.12 |
3.43 |
[0079] Comparing the first period (using formalin) of the campaign with the 2
nd period (with PAA) it is possible to see a reduction of about 10°F both on the clear
juice of 2
nd saturation and in the thin juice after the resins, in which the hardness value is
halved.
[0080] It is plausible to attribute the reduction of calcium salts to a lower presence of
organic acids on the depurated juice, justifiable with a lower inverted sugar content
in the diffusion juice - something that would also rule out the hypothesis of biological
destruction of the inverted sugar with the forming of acids.
EXAMPLE 2
[0081] For the sugar production campaign of the year after the one of Example 1, a similar
experimentation was carried out - this too of a duration equal to that of the whole
campaign - which saw the use, for practically the whole period, of the PAA system
(3%+15%) and Natural Vegetable Extracts (NVE) based on hop, palm kernel and pine resin
extracts.
[0082] For the whole campaign, no particular difficulties were found in controlling the
infections in all operating conditions encountered throughout the process, thanks
to the acquired familiarity in handling the PAA/NVE system.
[0083] From the point of view of controlling the infections, the vegetable extracts used
alone, in an intermediate period of the campaign of the duration of 15 days, performed
well, save for confirming the progressive loss of efficacy over time.
[0084] The PAA/NVE combination turned out to be an optimal technological choice both as
regards the control of infections, thanks to the contrasting effect with respect to
the establishment of resistant species, and also as regards the possibility of avoiding
the undesirable effect on press absorptions caused by the massive use of PAA concomitantly
with peaks of lactic acid in the juices.
[0085] The result was that it became possible to maintain the control parameters within
the ranges considered optimal, equivalent to 5.8-6.0 for the pH and 250-400 ppm (0.25-0.40
g/I, see Figure 2 for comparison) for the L-lactic acid formed.
[0086] The dry matter of the pressed spent pulps was virtually constant throughout the campaign
at values comparable to those of Example 1 when not, indeed, better than them, with
sampling points being equal. The best performances of the pressing station were confirmed
by higher electric absorption values than the ones recorded during the previous campaign
- indicating a better use of the machines that produced a quantity of pressed pulp
that was considerably higher than in the previous year.
[0087] The use of aluminium sulphate was totally avoided during the campaign period except
for the 15 days of trial with only vegetable extracts.
[0088] As regards chalk, the average dosage was around a value slightly lower than the average
value of the previous campaigns.
[0089] As also demonstrated by the experimental results shown for exemplificative purposes
above, the method for controlling bacterial infections based on the combined use of
PAA as the main antibacterial, fed into the system in a continuative manner, and of
NVE as a secondary antibacterial, to be used in a non-continuative manner, allows
having a complete advantage of the technological benefits linked to using peracetic
acid while, at the same time, controlling the development of PAA-resistant species
that can be effectively eliminated via sporadic targeted treatment with natural antibacterial
agents without interrupting the primary treatment.
[0090] The present invention has been disclosed with particular reference to some specific
embodiments thereof, but it should be understood that modifications and changes may
be made by the persons skilled in the art without departing from the scope of the
invention as defined in the appended claims.
1. A method for controlling bacterial infection in sugar production processes starting
from sacchariferous vegetable material, wherein to the sugary material to be treated
there is added one or more solutions based on peracetic acid and hydrogen peroxide,
as a primary disinfectant, at least one of which is fed in a continuative way to the
process, characterised by the fact that a further product, based on natural vegetable extracts compatible with
foodstuffs and having antibacterial activity, is added as a secondary disinfectant.
2. A method according to claim 1, wherein the said product based on natural vegetable
extracts is selected from the group consisting of: hop extract or one or more of its
constituents having antibacterial activity; vegetable resins compatible with foodstuffs
or one or more of their constituents having antibacterial activity; palm kernel extracts
or one or more of their constituents having antibacterial activity; or a mixture of
two or more of the said products.
3. A method according to claim 2, wherein the said product based on natural vegetable
extracts is hop extract, or a mixture of hop beta-acids or a mixture of hop alpha-acids.
4. A method according to claims 2 or 3, wherein the said product based on natural vegetable
extracts is a moderately alkaline aqueous emulsion containing 5-20% by weight of acids
or other natural compounds having antibacterial activity.
5. A method according to claim 4, wherein the said product based on natural vegetable
extracts is based on hop extract and contains 80-90% by weight of water, 1-3% by weight
of potassium hydroxide, 8-12% by weight of beta-acids, and 1-5% by weight of other
hop compounds.
6. A method according to any one of claims 1-5 for sugar beet production processes, wherein
of the said one or more solutions based on peracetic acid and hydrogen peroxide, a
first solution is added continuously in the press water system and a second solution
is added in the form of shocks in one or more of the following stages of the production
system: inside the diffusers, in the extraction juice system, in the juice-cossettes
mixer, in the juice-cossettes line.
7. A method according to claim 6, wherein the said solutions based on peracetic acid
and hydrogen peroxide contain 2-15% by weight of peroxyacetic acid and 15-50% by weight
of hydrogen peroxide.
8. A method according to claim 7, wherein the said solutions based on peracetic acid
and hydrogen peroxide also contain 5-25% weight of unreacted residual acetic acid
as well as 0.5-1.5% by weight of other acids used as stabilisers in the peracetic
acid manufacturing process.
9. A method according to any one of claims 6-8, wherein the said first solution based
on peracetic acid added continuously in the press water system is fed into the process
at a dosage ranging between 0.1 and 30 ppm of peracetic acid.
10. A method according to any one of claims 6-9, wherein the said second solution based
on peracetic acid is added as shocks with an average dosage ranging between 3 and
120 ppm of peracetic acid, and with a frequency ranging from 3 to 12 times a day.
11. A method according to any one of claims 6-10, wherein the said product based on natural
vegetable extracts compatible with foodstuffs and having antibacterial activity, used
in a non-continuative manner, is fed to the process on the onset of species resistant
to the peracetic acid-based disinfectant.
12. A method according to claim 11, wherein the said product based on natural vegetable
extracts is fed to the process as shocks with a frequency of between 1 and 6 times
a day and in dosages ranging between 5 and 50 kg of product per shock, until such
time as a pre-established decreased level of bacterial activity is detected.
13. A method according to any one of claims 6-10, wherein the said product based on natural
vegetable extracts compatible with foodstuffs and having antibacterial activity used
in a non-continuative manner is fed to the process for preventive purposes and at
pre-established time intervals.
14. A method according to claim 13, wherein the said product based on natural vegetable
extracts is fed to the process as shocks with a frequency ranging between 1 and 3
times a day and at dosages ranging between 5 and 20 kg of product per shock, one day
a week.
15. A method according to any one of claims 11-14, wherein the said product based on natural
vegetable extracts is fed to one or more of the following stages of the production
process: inside the diffusers, inside the extraction juice system, in the juice-cossettes
mixer, in the juice-cossettes line.