Grape juice, browning

Whey can be fortified with sucrose and fermented with yeast to yield an alcoholic whey. Upon freeze concentration, a whey liquor with 10 to 69% alcohol can be obtained. Alcohol fermentation carried out in whey supplemented with brown sugar yields a whey cordial (Baldwin 1868). Wine-like beverages have been made from whey, but they do not appear to be competitive with wines made from grape juice. 

M. Buglione and J. Lozano, Nonenzymatic browning and chemical changes during grape juice storage, J. Food Sci., 2002, 67, 1538-1543. 

White Table Wines. The free-run grape juice is the most important fraction used in white table wine production. To the juice will be added S02 at 75-150 mg/L, depending on the grape condition. Most winemakers prefer to add not over 100 mg/L. The primary purpose of the S02 is to prevent browning and retard growth of wild yeasts and other undesirable microorganisms. 

Acetic acid can be produced by the enzyme-catalyzed oxidation of ethyl alcohol. The brown acetic acid in vinegar is produced from fruit juices (apple or grape juice) and is known as natural acetic acid. 

Bozkurt, H., G6gii , F., and Eren, S. Nonenzymic browning reactions in boiled grape juice and its models during storage. Food Chem., 64, 89, 1999. 

Indirect evidence of the involvement of free carbonyl groups in the browning of fruit juices is provided by the work of Markh (1950). He showed that apple and grape juices, when heated with added amino acids, became colored, presumably owing to formation of melanoidins. Color production could be prevented by fermentative removal of sugars or by their inactivation by reaction with sulfurous acid. 

The anthocyanin stabilities of grape-marc, elderberry, and black currant extracts were lower in all sucrose (100 g/L)-added systems as compared to the controls at pH values of 3, 4, and 5, whereas the brown index did not change with the addition of sugar. On the contrary, a protective effect of 20% sucrose added to frozen crowberries and strawberries was reported and the stabilities of anthocyanin juices from aronia were higher in syrups than in diluted extracts. Roselles pre-... 

UF is used to clarify various fruit juices (apple, grape, pear, pineapple, cranberry, orange, lemon) which are recovered as the permeate [Blanch et al., AlChE Symp. Ser. 82, 59 (1986)]. UF has also been used to remove pigments and reducing browning in wine production [Kosikowski in Membrane Separations in Biotechnology, McGregor (ed.), Marcel Dekker, New York, 1986]. 

Phenolic compounds are of interest due to their potential contribution to the taste (astrin-gency, bitterness, and sourness) and formation of off-flavor in foods, including tea, coffee, and various fruit juices, during storage. Their influence on the appearance of food products, such as haze formation and discoloration associated with browning in apple and grape products, is also significant. Furthermore, analysis of these phenolic compounds can permit taxonomic classification of the source of foods. The importance of each phenolic compound and its association with the quality of various foods is described further in Sec. IV, on food applications. 

Contrary to expectations that fungal diseases would lead to elevated levels of PR proteins in berries, Marchal et al. (1998) observed that juice from berries infected by B. cinerea showed reduced protein levels, and suggested that proteolytic enzymes from B. cinerea were responsible for this. Secretion of proteases by B. cinerea has been observed in culture media and on fruits such as apple (Zalewska-Sobczak et al. 1981) and tomato (Brown and Adikaram 1983). Girbau et al. (2004) also examined the impact of infection of grapes with B. cinerea in the vineyard and showed that infection resulted in marked decreases in the levels of PR proteins in... 

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