Synthesis of fruity ethyl esters by acyl coenzyme A: alcohol acyltransferase and reverse esterase activities in Oenococcus oeni and Lactobacillus plantarum.

AIMS: To assess the abilities of commercial wine lactic acid bacteria (LAB) to synthesize potentially flavour active fatty acid ethyl esters and determine mechanisms involved in their production. METHODS AND RESULTS: Oenococcus oeni AWRI B551 produced significant levels of ethyl hexanoate and ethyl octanoate following growth in an ethanolic test medium, and ester formation generally increased with increasing pH (4.5 > 3.5), anaerobiosis and precursor supplementation. Cell-free extracts of commercial O. oeni strains and Lactobacillus plantarum AWRI B740 were also tested for ester-synthesizing capabilities in a phosphate buffer via: (i) acyl coenzyme A: alcohol acyltransferase (AcoAAAT) activity and (ii) reverse esterase activity. For both ester-synthesizing activities, strain-dependent variation was observed, with AcoAAAT activity generally greater than reverse esterase. Reverse esterase in O. oeni AWRI B551 also esterified 1-propanol to produce propyl octanoate, and deuterated substrates ([(2)H(6)]ethanol and [(2)H(15)]octanoic acid) to produce the fully deuterated ester, [(2)H(5)]ethyl [(2)H(15)]octanoate. CONCLUSIONS: Wine LAB exhibit ethyl ester-synthesizing capability and possess two different ester-synthesizing activities, one of which is associated with an acyl coenzyme A: alcohol acyltransferase. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrates that wine LAB exhibit enzyme activities that can augment the ethyl ester content of wine. This knowledge will facilitate greater control over the impacts of malolactic fermentation on the fruity sensory properties and quality of wine.

Evaluation of gene modification strategies for the development of low-alcohol-wine yeasts.

Saccharomyces cerevisiae has evolved a highly efficient strategy for energy generation which maximizes ATP energy production from sugar. This adaptation enables efficient energy generation under anaerobic conditions and limits competition from other microorganisms by producing toxic metabolites, such as ethanol and CO(2). Yeast fermentative and flavor capacity forms the biotechnological basis of a wide range of alcohol-containing beverages. Largely as a result of consumer demand for improved flavor, the alcohol content of some beverages like wine has increased. However, a global trend has recently emerged toward lowering the ethanol content of alcoholic beverages. One option for decreasing ethanol concentration is to use yeast strains able to divert some carbon away from ethanol production. In the case of wine, we have generated and evaluated a large number of gene modifications that were predicted, or known, to impact ethanol formation. Using the same yeast genetic background, 41 modifications were assessed. Enhancing glycerol production by increasing expression of the glyceraldehyde-3-phosphate dehydrogenase gene, GPD1, was the most efficient strategy to lower ethanol concentration. However, additional modifications were needed to avoid negatively affecting wine quality. Two strains carrying several stable, chromosomally integrated modifications showed significantly lower ethanol production in fermenting grape juice. Strain AWRI2531 was able to decrease ethanol concentrations from 15.6% (vol/vol) to 13.2% (vol/vol), whereas AWRI2532 lowered ethanol content from 15.6% (vol/vol) to 12% (vol/vol) in both Chardonnay and Cabernet Sauvignon juices. Both strains, however, produced high concentrations of acetaldehyde and acetoin, which negatively affect wine flavor. Further modifications of these strains allowed reduction of these metabolites.

Eating as both coping and stressor in overweight control.

AIM: The aim of this study was to test a conceptual model proposing that stress evokes eating as coping, that eating then becomes a stressor in itself, and that a coping repertoire specific for overeating is required to moderate its yield of negative mood states. BACKGROUND: It is known that stressors may evoke eating as a coping response, and that some persons respond to lapses in their dietary regimen with depression and self-criticism. These two findings are linked within the context of a stress and coping paradigm that has in the past been applied to the study of substance abuse. METHOD: A survey of 79 women who reported overeating was implemented, including the administration of five instruments and a telephone interview. FINDINGS: Over 43% of the variance in the dependent variable, negative mood states, was explained by hierarchical regression of the independent variables, entered sequentially as exemplars of: social stressors, coping, degree of required calorie consumption, use of overweight control strategies and the interaction between the degree of required weekly calorie consumption and use of overweight control strategies. Significant contributions were made by variables denoting stressors, coping, and the interaction between degree of required calorie consumption and use of overweight control strategies. Of particular interest was the suggestion that for individuals who frequently use strategies to control overeating and overweight, eating may produce negative mood states. Individuals intensively involved in efforts to control their weight may be vulnerable for dysphoria, may require unique nursing interventions, and thus deserve continued study in this context.

Weight differences in emotional responsiveness to proprioceptive and pictorial stimuli.

Two studies were conducted to investigate weight differences in emotional responsiveness to proprioceptive and pictorial stimuli. Contrary to past evidence that overweight persons are more emotional than normals, the emotional state of normal-weight subjects fluctuated with manipulations of their facial expression, whereas that of overweight subjects did not respond to these proprioceptive cues. Furthermore, whereas past research employing affectively loaded pictures had found overweight persons to be more emotionally responsive than normals to these external stimuli, no weight differences were obtained in the present studies, which employed less polarized pictures. Implications of these findings for generalizations about weight differences in emotionality are discussed.