The effect of juice clarification, static or rotary fermentation and fining on ochratoxin A in wine

Semillon and Shiraz grapes containing ochratoxin A (OA) were produced by inoculation of bunches on the vine with Aspergillus carbonarius. Small scale vinification of these grapes was performed and the OA content at various stages was analysed. Semillon must was treated with pectolytic enzymes and the juice after pressing was fined with bentonite. Neither pectolytic enzymes nor bentonite influenced the OA content of the clarified juice. Shiraz must was vinified by either static or rotary fermentation. No differences in the OA content of wine after pressing were noted. OA was concentrated in juice lees and gross lees. However, additional juice or wine recovered from lees after centrifugation did not display increased OA contamination compared to racked juice or wine. Addition of bentonite at 2.5 g/L to a Semillon wine containing 56 mg grape-derived protein/L and ca. 8 μg OA/kg resulted in a 67% reduction in OA concentration. Potassium caseinate showed some effect, whereas gelatin, isinglass and PVPP did not significantly diminish OA in white wine compared to wine settled without fining agents. Addition of yeast hulls at 5.0 g/L to a Shiraz wine containing ca. 5 μg OA/kg yielded a 43% reduction. Gelatin was also slightly effective. Storage of wine for 10-14 months resulted in a decrease in OA concentration of 22% and 29% for white and red wines, respectively.Su-Lin l. Leong, Ailsa D. Hocking and Eileen S. Scot

Produção de álcoois superiores por linhagens de Saccharomyces durante a fermentação alcoólica Production of higher alcohols by Saccharomyces strains during alcoholic fermentation

A produção de álcoois superiores pelas leveduras Saccharomyces cerevisiae M-300-A, Saccharomyces uvarum IZ-1904 e levedura de panificação (Saccharomyces cerevisiae) foi estudada em diversas condições de temperatura, concentração de sacarose, pH, fontes de nitrogênio e com inibidor 2-4 dinitrofenol (DNP). Em todas as condições estudadas, a levedura Saccharomyces uvarum IZ-1904 apresentou a menor formação de álcoois superiores enquanto a levedura de panifícação apresentou os teores mais elevados. Com o aumento de temperatura e da concentração de sacarose ocorreu maior formação de álcool isoamílico pelas leveduras estudadas. Em pH 4,5 ocorreu menor produção de álcoois superiores do que em pH 3,0. Na presença do inibidor DNP ocorreu significativa redução (p< 0,05) nos teores de álcool isoamílico. As leveduras utilizadas não apresentaram o mesmo comportamento em relação ao sulfato de amônio e uréia quanto a formação de álcoois superiores.<br>The production of higher alcohols by Saccharomyces cerevisiae M-300-A, Saccharomyces uvarum IZ-1904 and baker's yeast (5. cerevisiae) was studied under several temperature conditions, sucrose level, pH, nitrogen sources and with 2-4 dinitrophenol (DNP). The yeast IZ-1904 showed lower production of higher alcohols than other yeasts in all conditions studied. With the increase of temperature and higher level of sucrose an increase of isoamyl alcohol production was observed. A lower formation of higher alcohols was observed at pH 4.5 than at pH 3.0. With the addition of DNP occurred a significant reduction in isoamyl alcohol content. The yeasts did not show the sanie production of higher alcohols in relation to urea and ammonium sulfate