50 March/April 2011

PROCESS TECHNOLOGY • BENTONITE • CLARIFICATION • FILTRATION •KIESELGUHR • STABILIZATION •

In order to meet market requirements and ensure eco-nomic success, producers of fruit juices and fruit juiceconcentrates and their suppliers have to get to gripswith changing consumer expectations and everstricter product specifications. Anyone who fails tomeet these expectations and specifications will become less competitive.

BENTONITE UNDER DISCUSSION

The name bentonite was derived from the place where itwas first found near Fort Benton, Wyoming (USA). Itsamazing characteristics are principally determined by theclay mineral Montmorillonite. This name is derived fromthe Southern French town of Montmorillon, where theseclays also occur. The mineral Montmorillonite is charac-terized by high water-absorbing and swelling capacity.Since it is found in the earth’s crust, it naturally also con-tains other minerals such as quartz, mica, feldspar, pyriteand calcite. Montmorillonite is generated by weatheringof volcanic ash. In addition to substitutable ions (Na, Ca),bentonite also contains small quantities of heavy metals.The International Code for Wine Treatment Agents speci-fies maximum limits for soluble ions in bentonites thatare used in beverage production. No such code exists forfruit juices.

Bentonite is under discussion in view of the possibility thatit may contaminate fruit juices with undesired ions andother substances. Earlier reservations relating to iron con-tent and an associated risk of hazing have been supersed-ed by the issue of potential heavy metal contamination.

The discussion was triggered by an article published inthe German Ökotest magazine back in 1977, reportingsmall quantities of uranium in apple juice spritzer. Sincethen, the industry has sought ways and means to reduceor eliminate such contamination. Later it turned out thatthe uranium originated mainly from the mineral waterand only to a very small degree from the other raw mate-rials used for the spritzer. Despite the fact that the quan-tities found were significantly lower than the safe loadfor mineral water of 15 ppb (parts per billion), manufac-turers of spritzer raw materials have since been faced

NEW FINDINGS ON CLARIFICATION,

STABILIZATION AND FILTRATION OF FRUIT

JUICES AND FRUIT JUICE CONCENTRATES

with demands for a maximum limit of 1 ppb. Discountersand research labs are both striving towards halving thelimits for a range of undesired substances such as heavymetals, HMF (hydroxymethylfurfural), patulin and pesti-cides in fruit juices.

The focus is on the following questions:

1. Can the use of bentonite be avoided altogether, and arepractical replacement products or processes availablethat would make its application unnecessary in future?

2. Do different conditions and processes lead to a changein the migration characteristics of heavy metals andother undesired substances from bentonite into thejuice?

When applied in high doses and under unfavourable con-ditions, bentonite can increase the heavy metal content byup to 5 ppb. Although this is still far below the current lim-it for mineral water, the requirement stipulated by themarket of less than 1 ppb is still not met. The followingfindings can be derived from a range of trials that exam-ined heavy metal migration from bentonite under cold andhot clarification conditions. The maximum quantity ofheavy metals migrating into the juice from SIHA Ca-Bentonite and SIHA Active Bentonite was 1 ppb. To verifythe suitability of SIHA Ca-Bentonite for hot filtration it isadvisable to carry out laboratory tests. SIHA ActiveBentonite can be used for hot filtration without restriction.

Heavy metals are not firmly bonded to bentonite and caneasily be flushed out with water. By increasing the waterquantity during pre-swelling and subsequently decantingof the supernatant liquid, the heavy metal content of thebentonite prepared for application can be reduced signif-icantly. Any heavy metals dissolved in the pre-swellingwater are removed by discarding the supernatant liquid.

ALTERNATIVES TO BENTONITE

In the quest for alternatives, the following substanceswere examined that are used in the beverage sector andthe food industry.

S Hagemann, R. Junker, C. Prinz

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51March/April 2011

Silica gels (amorphous silicon oxide for ad-sorption of protein substances) are unreliablefor the purpose of stabilization and can onlybe used for complementary residual stabi-lization.

Acrylic polymers with macroporous structurefor protein adsorption can only be used infully clarified and prefiltered juice. Highcolour adsorption limits their application inred juice and apple juice spritzer.

China clay and titanium dioxide, which areused as food additives E171 and E559, arepractically ineffective.

Proteases (enzymes that are able to split pro-teins or peptides) are currently under closescrutiny. They may present an opportunityfor the fruit juice sector, where, in contrast tothe wine sector, the application of proteasesis permitted.

Filter additives with negative zeta potentialproved effective, but have not yet achievedthe high stabilization performance of ben-tonites. This product line offers significantdevelopment potential.

In summary, it is currently not possible toavoid the use of bentonite for stabilization.Undesired contamination of products can bereduced significantly by using an appropri-ate, top-quality and cleaned bentonite, andby selecting suitable process parameters suchas the volume of pre-swelling water, stirringand maceration times and process tempera-tures.

VISION OF FULL CONCENTRATE STABILIZATION

In 2009 the price of AJC reached a historiclow, while at the same time heating oil pricesreached record highs. This fact illustrates thesignificance of continuous process optimiza-tion for reaching or maintaining competi-tiveness.

The production of highly stable, ready-to-fillconcentrates requires these products to bere-diluted to 20 °Brix and then highly con-centrated to 70 °Brix, following stabilization.If this process step could be avoided, it wouldnot only reduce process times but also cutthe energy costs associated with re-concen-tration significantly.

PROCESS TECHNOLOGY

Figs. 1 – 3: Heavy metal content in apple juice (mg/l) after treatment with 100, 200 and300 g of bentonite/hl

FIG. 4: OVERVIEW OF ALTERNATIVES TO BENTONITE

ProductClarificationflocculation

Stabilization Adsorption of anthocyaninsBentotest H/K test Gushing

Bentonite +++ +++ +++ +++ +

Silica gel ± ±-++ ±-++ ±-+ +

Protein absorber - +++ +++ +++ +++

Filter additive ± +++ ++ + +

White clay + + + + +

Titanium dioxide - - - - -

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The test results shown in Figs. 5 and 6indicate that full concentrates can bestabilized with activated carbon andbentonite. In a field test the colourreduction achieved with SIHAActivated Carbon FA was 0.188 ab-sorbance units at a dosage of 1 kgactivated carbon per tonne of AJC. Insemi-concentrate the value was0.239. The effect in full concentratewas reduced by 21 %. Stabilizationwith silica gel was not possible.Compared with the stabilization ofsemi-concentrate (20 – 24 °Brix), thetested polyphenol and protein adsor-bers exhibited only 2 – 4 % of theusual performance (1 – 2 bed vol-umes compared with 50 bed volumesor more).

Fig. 6 indicates that the bentonite SI-HA PURANIT eliminates turbidity-forming proteins and is highly effec-tive in preventing gushing in full con-centrate. This means that it is requiredin many cases. Both treatment media,activated carbon and bentonite, canbe used in combination and have tobe separated again through filtrationwith kieselguhr. Separation of SIHAActivated Carbon via kieselguhr filtra-tion was straightforward, while ben-tonite blocked the filtration atdosages of more than 250 g pertonne.

HMF formation in full concentratedepends on the temperature andholding time. Treatment mediashould be applied in the temperaturerange of 50 – 70 °C, since HMF for-mation is limited in this range. Short-term temperature increases to 80 °Cfor separation of treatment mediathrough kieselguhr are acceptable.

USEFUL INDICES FOR STERILE FILTRATION (ACB, TAB) OF FULL CONCENTRATE

In the past, viscosity tables were anessential basis for the configurationof filter systems for ACB filtration.Compared with standard sheets, the

Viscosity is exponential to the temperature and concentration. Full concen-trates are therefore highly viscous. This can be counteracted by increasingthe temperature and associated exponential reduction in viscosity. The fol-lowing questions are therefore of interest:

1. Is there a temperature range for full concentrates that allows economicfiltration while avoiding the negative consequences associated with tem-perature increases?

2. Are treatment media such as bentonite and activated carbon effective athigh viscosity, and is the concentrate still able to enter the pores ofmacroporous adsorbents such as silica gel or adsorbers?

3. What is the situation regarding the formation of HMF, if the temperatureis increased in order to reduce viscosity?

FIG. 6: STABILIZATION OF APPLE JUICE FULL CONCENTRATE WITH ACTIVATED

CARBON AND BENTONITE

SIHA Activated Carbon FA Dosage (g/t)

1000 1000 1000 1000 1000

SIHA PURANIT Dosage (g/t) 0 250 500 750 1000

NTU increase during heat/cold test + 4,1 + 2,2 + 0,9 + 0,2 + 0,4

Gushing test; Time (min:sec) until foam collapses totally

> 10:00 3:35 0:30 0:40 0:20

Fig. 7: HMF formation in AJC (70 °Brix, 32 g acid/kg as citric acid) as a function of tempera-ture and holding time

Fig. 5: Decolourization and stabilization of AJC (70 °Brix) with SIHA Activated Carbon FA

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NEW LABELLING FOR KIESELGUHR

EU directive no. 1272/2008 for the classification, la-belling and packaging of substances and mixtures (CLPordinance) came into effect on 20 January 2009. It inte-grates the classification criteria of the United NationsGlobal Harmonized System (GHS) in EU law. The CLP ordi-nance will gradually replace the directives on hazardoussubstances (directive 67/548/EEC) and on hazardouspreparations (directive 1999/45/EC).

According to the CLP ordinance, manufacturers of sub-stances and mixtures are required to classify, label andpack their products based on the new ordinance from 1December 2010 and 1 June 2015 respectively. The safetydata sheets also have to be adapted. According to the CLPordinance there are transitional regulations for productsthat were classified, packed and distributed with the ‘old’labelling before 1 December 2010, allowing such productsto be sold until 30 November 2012 within the EU.

March/April 2011

newly developed BECOPAD depth filter medium indicat-ed promising improvements in terms of flow rate, macer-ation time and germ retention, so that further trials werecarried out. They showed the significant potential thatcan be explored with BECOPAD. Standard sheets do notoffer such technical opportunities.

The tests were carried out with a 72 °Brix apple juiceconcentrate that was subjected to sterile pre-filtration inorder to avoid blockages during the test series. BECOPAD550 and 580 was used for prefiltration. BECOPAD 350and 270 was used for sterile filtration. Tests were carriedout in a temperature range between 15 – 80 °C. The pre-filtration can be carried out at a temperature of 30 °C,both with standard filter sheets or with the BECOPADdepth filter medium. Prefiltration with BECOPAD 580 ispossible from 15 °C. Sterile filtration with BECOPAD 270and 350 is possible from 45 °C, whereas standard filtersheets require a minimum temperature of 60 °C. If thedifferential pressure is increased from 1.5 to 3.0 bar, ster-ile filtration of full concentrate could even be realised at30 °C, if BECOPAD 580 is used in combination with BECOPAD 270.

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dust from plant-based substances and minerals shouldbe avoided.

SUMMARY

It is currently not possible to substitute bentonite withother stabilizers. Undesired bentonite contamination ofjuice can be reduced through skilful handling. Increasedenergy costs and intensified competition necessitatecontinuous process optimization. Full concentrate stabi-lization and filtration can reduce energy costs signifi-cantly. Through application of treatment media withinthe right temperature range, temperature-related HMFformation remains within acceptable limits. The new BE-COPAD depth filter medium opens up new opportunitiesfor quality-preserving and cost-cutting sterile filtrationof full concentrates. Kieselguhr no longer has to be labelled as a hazardous substance in future.

WHAT DOES THIS MEAN FOR KIESELGUHR?

Many years ago, kieselguhr producers voluntarily decidedto label crystalline silicic acid as ‘Xn Harmful’ in conjunc-tion with R-phrases R 20 (Harmful by inhalation) and R48 (Danger of serious damage to health by prolonged ex-posure). No grading/classification according to directive67/548/EEC was undertaken. Studies relating to risk as-sessment and potential health effects of respirable, crys-talline silicic acid were carried out within the frameworkof the CLP ordinance and REACH directive (EC) no.1907/2006 for the Registration, Evaluation, Authorisationof Chemical Substances.

Based on the results of these studies, respirable, crys-talline silicic acid (respirable quartz and cristobalite, sub-sequently referred to as RCS) was classified as:

• STOT RE 1, if the RCS concentration is 10 % or higher,• STOT RE 2, if the RCS concentration is between 1 and 10 %. (STOT = specific target organ toxicity; RE = repeated exposure)

Risk classification is not required if the RCS ratio in aproduct is less than 1 %.

The RCS ratio in products depends on the ratio of crys-talline silicic acid and its grain size distribution. Fine par-ticles are far more likely to penetrate deep into the lungsthan coarse particles, thereby posing a health risk.BECOGUR kieselguhrs were examined using the relevantscientific techniques, with a view to reclassify the prod-ucts. Despite the fact that some products contain crys-talline silicic acid, these particles are relatively large, sothat the respirable ratio is low. The measurementsshowed that all BECOGUR types had less than 1 % RCS.For this reason they no longer require risk classificationor warning labels. Nevertheless, we still regard it as im-portant to alert users to the fact that the inhalation of

AUTHORS

Dipl.-Ing. Rainer JunkerSales Manager Fruit Juice & Spirits

Christian PrinzProduct Manager Biotechnology – Food & Beverage

Dipl.-Ing. Sven Hagemann(FH), Product Manager BeverageTechnology – Food & Beverage

BEGEROW D-55450 Langenlonsheim – Germany

www.begerow.com

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