Beer and Wine Production - American Chemical Society

Chapter 11

Ultrafiltration A New Approach for Quality Improvement of Pressed Wine A. J. Shrikhande and S. A. Kupina

Downloaded by MONASH UNIV on February 29, 2016 | http://pubs.acs.org Publication Date: August 23, 1993 | doi: 10.1021/bk-1993-0536.ch011

Heublein Wines, 12667 Road 24, Madera, CA 93639

The pressed wines are an integral part of grape processing and vary in quality depending upon pressing practices. Pressed wines are inferior to free run wines due to their higher polyphenol content. The principal phenolic compounds responsible for the astringency and bitterness in pressed wines are procyanidins. Ultrafiltration is a superior alternative to conventional fining treatments and anion exchange for quality improvement of pressed wines. Ultrafiltration was found to be more selective in removing pressed character while retaining most of the wines original varietal characteristics. Profiles of the phenolics were obtained on High Performance Liquid Chromatography ( H P L C ) which was necessary for optimizing the ultrafiltration process for pressed wines.

Ultrafiltration Process Technology was investigated for wines which were characterized as intolerably harsh and astringent with strong pressy character. The objective was to develop a suitable technology to reduce harshness from these wines while maintaining sufficient fruitiness to enable blending of these wines as standard white wines. Many classical approaches, including gelatin fining and anion exchange, were also evaluated for quality improvement of these wines. Gelatin fining at a rate of 10-15 lb/1000 gallons was needed to decrease harshness. This treatment also reduced the fruity character of wines and resulted i n an unmanageable increase in lees volume and bentonite requirements. Anion exchange technology as well as a number of polymeric adsorbents proved futile and resulted in complete loss of fruitiness in pressed wines. 0097-6156/93/0536-0197$06.50/0 © 1993 American Chemical Society

In Beer and Wine Production; Gump, Barry H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1993.

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A l l of the approaches mentioned above fell short of expectations and necessitated a novel approach which would selectively remove harsh components without appreciably affecting the fruitiness of pressed wines. This research was successful in the application of an Ultrafiltration Technology for selectively reducing harshness and astringency while substantially maintaining the fruity character of hard pressed white wines. This report describes the detailed research efforts made towards the applications of the Ultrafiltration Membrane Technology for the quality improvement of wines.


Chemistry O f Pressed Wines The pressed wines are an integral part of grape processing and vary in quality and quantity depending upon the handling and pressing practices. Pressed wines are generally inferior to free run juice wines due to their higher polyphenol content. It is also generally recognized that longer the contact time of grape juice with skins and seeds, the larger the concentration of phenolics that are extracted into the wine. The principal phenolic compounds responsible for the astringency and bitterness in wines are classified in the general group called flavonoids. A flavonoid is any compound containing a carbon-15 three ring base structure.

Basic Flavonoid Structure The modification of central ring defines the subclassification. These compounds are exclusively found in the skins, seeds and stems of grapes. Approximately one-third are found in the skins and two-thirds are found in the seeds (1). The two major subclasses of flavonoid that cause bitterness are flavonols and flavan-3-ols. The flavonols have the following basic structure.

Flavonol


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SHRIKHANDE & KUPINA

Ultrafiltration of Pressed Wine

199


The typical compounds in this category known to be present in grape skins are rutin, quercetin, quercitrin, myricitrin and kaemferol. These compounds are associated with the bitterness of wine and range in molecular weight from 300-600. The other category called flavan-3-ol is perhaps more important i n wines and also responsible for bitter sensations.

OB

Flavan-3-ol The flavan-3-ol monomelic compounds such as (+)-Catechin, (-)Epicatechin, (+)-Gallo-catechin (-)-EpigaUocatechin are only found in the skins and the seeds of grapes. The molecular weight of these compound is i n the vicinity of 300. Perhaps the most important group of flavonoid compounds found in wines belong to a polymerized form of flavan-3-ol. These compounds in enological research are referred to as procyanidins (7). These compounds are abundant in skins and seeds and get extracted in grape juice depending upon the severity of processing conditions. The degree of polymerization of these compounds varies from simple dimers, trimers to heptamers (3-4). The following structures are examples of a dimer and a trimer.

OH

Dimer




200

Trimer The molecular weight of these compounds varies from 600 for the dimers to 2100 for a heptamer. The total phenolics present in wines also include some compounds referred to as non-flavonoid. These phenolic compounds are commonly referred to as cinnamates. CH«CH-COOH

Cinnamic Acid The four major cinnamic acid derivatives have been reported in white wines and they are caffeoyl tartaric acid, p-coumaryl tartaric acid, caffeic acid and p-coumaric acid (5-6). It has been shown that cinnamates are largely confined to the free run juice. They, therefore, constitute a much higher proportion of the total phenols of white wines and appear to be a major class of phenols in white wines made without pomace extraction. In comparison to the flavonoid compounds, the flavor effects of cinnamates in white wine are evidently mild. The molecular weight range of cinnamates in white wine varies from approximately 160 to 400. In wine tastings, the sensations of astringency and bitterness are frequently confused. Astringency is identified as a puckery tactile mouthfeel


11. SHRIKHANDE & KUPINA


201

sensation while bitterness is a true taste sensation. Recently, L e a and Arnold (4) had defined these sensations more critically.


Astringency. Is believed to result from non-specific and somewhat irreversible hydrogen bonding between o-diphenolic groups and protein in the mouth, thereby causing the distinctive drying and puckering sensation which is difficult to remove and makes further taste assessment a problem. The larger the procyanidin concentration, the greater its capacity for hydrogen bonding and more astringency will be perceived. Bitterness. Is regarded as being due to an interaction between polar molecules and lipid portion of the taste papillae membrane and hence it is critically dependent on the relative lipid solubilities of the bitter materials. In the case of procyanidins, only the smaller molecules (up to tetramers) would be sufficiently fat soluble to pass in the lipid membrane and interact suitably with taste receptors to produce the phenomenon of bitterness. The following conclusions have been drawn by L e a and Arnold (4) about the relationship of astringency and bitterness associated with monomelic catechins and polymeric procyanidin compounds. 1. 2. 3.

Astringency is predominately associated with the procyanidins that have a degree of polymerization greater than four. Bitterness is associated with monomelic catechins and procyanidins with degree of polymerization up to tetramer. There is no one procyanidin which is exclusively bitter and another which is exclusively astringent.

Singleton and Noble (2) suggested that the balance of bitterness and astringency in wines was concentration dependent too, so that the perceived bitterness is masked by a greater perceived astringency as the total procyanidin content increases. Definition O f Ultrafiltration Ultrafiltration ( U F ) is a process where a semi-permeable membrane separates the components of the liquid/solute mixture according to their molecular size. In ordinary filtration, the process liquid flows perpendicular to the filter; in ultrafiltration the process liquid flows tangential to the membrane. The basic principle of the ultrafiltration operations is illustrated in Figure 1. The solution containing two solutes flows tangential to the membrane; one solute's molecular size is too small to be retained by the membrane and the other is of larger size allowing retention by the membrane. A hydrostatic pressure is applied to the upstream side of the supported membrane and the solvent containing the small molecule solute passes through the membrane while larger molecular solute is rejected or retained by the membrane. A feature of ultrafiltration, perhaps unique among filtration processes, is the ability to operate with steady filtration fluxes in absence of an external



202


)

Pressurized solution of harsh wine

••I ••I

> · · * · · . Membrane

• a · ·

· ··W ·

· · ·

Molecul es of large tannins (concentrate)

• ·· · A· A _

• • •• · ·· ·· ·· W

Wine without large tannins (permeate)

Figure 1. Schematic diagram of membrane ultrafiltration process. (Reproduced with permission from ref. 9. Copyright 1977 Marcel Dekker, Inc.)


11. SHRIKIIANDE & KUPINA


means for clearing the filter of accumulated solids. In ultrafiltration, the retained material always concentrates at the membrane-solution interface but is swept away by fluid dynamic forces. The retained particle size is one characteristic distinguishing ultrafiltration from other filtration processes. Viewed on a spectrum of membrane separation processes, ultrafiltration is one of the membrane methods that can be used for molecular separations. In Figure 2, membrane size filtration is shown as a function of filtration flux. A t the low flux end of the spectrum lie the commercial cellulose acetate reverse osmosis membranes with the capability of retaining sodium and chloride ions. Next come ultrafiltration membranes with the pores that span a range of 10" to 10' μπι (10-100 À) with filtration fluxes of about 0.5-10 gallons per square foot per day ( G F D ) per pound per square inch of driving pressure. Ultrafiltration membranes are commercially available for the molecular retention or separations in the range of 500 to 100,000 molecular weight cut offs. Microporous filters capable of virus and bacteria retention cover the size range of about .01-1.0 um with fluxes of 10-1000 G F D . Finally, conventional filters for normal particulate materials are capable of filtering particles of 1 μπι or larger with filtration fluxes above 1000 G F D . 3


203

2

Ultrafiltration Applications. The single largest application of U F has been i n the processing of cheese whey. Ultrafiltration is used for the recovery of whey proteins as a by-product. Ultrafiltration is also being successfully used for apple and pineapple juice clarification and is also being commercially used for enzyme, blood plasma, vaccine, hormone and variety of biomolecular separations. Ultrafiltration Concept For Pressed Wines. Before considering U F for pressed wine it was relevant to study the molecular weight composition of pressed wine components (Table I) irrespective of percent composition of each fraction. The basic difference between the free run juice wine and pressed juice wine is due to higher concentrations of harsh and astringent phenolic compounds emanated from the skin and seeds in pressed juice. These compounds vary i n molecular weight from 600-2000 and are the largest size molecular species i n clarified wine. These compounds are far separated in wine from other phenolics ranging i n molecular size between 200-500 and from sugars, acids, alcohol and aroma compounds which are in the vicinity of 200 molecular weight. In free run juice wines, the harsh and astringent compounds are present i n low concentrations due to minimum contact with seeds and skins. It was postulated that ultrafiltration with proper molecular membrane cut off i n the vicinity of 1000 could selectively remove these larger harsh and astringent phenolic compounds without appreciably affecting the other basic wine components. With this basic premise of eliminating harsh and astringent phenolic compounds from pressed wine, the ultrafiltration selective membrane concept was explored and development proceeded into a feasible technology for wine processing.



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ELECTRON MICROSCOPE

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H T HYDR06EN

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10 - 3

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FLUX (fftf/pfl

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MI CROP MOUS FILT

10'

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CONVENT1 )NAL PARTI CL FILTERS

10^

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Figure 2. Pore size vs. flow rate for separation media. (Reproduced with permission from ref. 9. Copyright 1977 Marcel Dekker, Inc.)

MOLECULE

CHLORIDE ION-

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3 GLUCOSE Ο MOLECULE— hi

2 β

2

STARCH MOLECULE

F-

TOBACCO MOSAIC VIRUS-

INFLUENZA VIRUS

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RED BLOOD CELLS-

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11. SHRIKIIANDE & KUPINA


205

Table I. Wine Composition as Related to Molecular Weight of Components Wine Component

Molecular Weight

water

18

alcohol

46

reducing sugars

180

acids

150

aroma compounds

Beer and Wine Production - American Chemical Society

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