Anastrepha fraterculus (Wiedemann), a pest of great economic importance in South America, needs urgently to be controlled by environmentally friendly methods such as the sterile insect technique for which mass rearing of insects is required. Because oogenesis takes place during the adult stage, mass-rearing facilities should provide the females a diet that maximizes egg production at the lowest cost. Accordingly, we investigated the effect of artificial protein sources in the adult diet (yeast derivatives of different cost but with similar amino acids profiles, and the addition of wheat germ) on fecundity. Additionally, we evaluated different ratios of yeast derivatives or wheat germ on ovary maturation, fecundity, and fertility as well as their association with the nutrient content of females. Females fed hydrolyzed yeast and yeast extract attained the highest fecundity level, and those fed brewer's yeast the lowest. Reducing the amount of hydrolyzed yeast, an expensive protein source, in the diet negatively affected fecundity and ovary maturation. Increasing the amount of brewer's yeast, a low-cost protein source, did not favor fecundity. The addition of wheat germ in the adult diet improved fecundity regardless of the yeast derivate considered. Percentage of egg hatch was not affected by the diet. Nutrient content of A. fraterculus females varied according to the adult diet provided and mating status. Our findings provide novel baseline information to understand the role of nutrition on reproductive performance of A. fraterculus females and are discussed in the context of resource allocation. They also provide valuable advances in the search for cost-effective adult diets at fruit fly mass rearing facilities.

Water soluble autolysate of yeast, usually utilised for microbial growth support, was used as additive in yoghurt fermentation. The yeast extract (YE) resulted in a decrease of fermentation time by 21% to reach a pH of 4·6. However, the YE resulted in unacceptable flavour and taste. By size exclusion chromatography, a fraction of the YE was obtained that could account for the observed 21% decrease in fermentation time. The fraction contained molecules of low molecular weight, consisting of minerals, free amino acids and peptides. The acceleration of the yoghurt fermentation was ascribed to the short peptides in the fraction. It is proposed that the application of this extract in industrial yoghurt manufacture would result in savings for both the industry and the consumer.

Yeast extract was used as a nutrient for growing lactobacilli in reduced-fat Cheddar cheese as early growth of non-starter lactic acid bacteria (NSLAB) in Cheddar cheese is suppressed by pasteurization of milk and the hostile environment of the cheese. Reduced-fat Cheddar cheese was manufactured from 100 kg standardized milk on two occasions. After milling, the curd was divided into two portions, C and E. To control portion, C, salt was added at normal levels. A mixture of salt and yeast extract was added to the experimental, E. The cheeses were ripened for 7 months at 8 °C and assessed for proteolysis and NSLAB growth during ripening. Mean % moisture, fat, protein, salt and pH were 40·6, 20·5, 31·1, 1·72 and 5·22 respectively, in E cheeses, and 39·5, 20·5, 30·9, 1·68 and 5·22, respectively, in C cheese. NSLAB counts in E cheeses were 101, 103, 105 cfu/g compared with 0, 101, 104 cfu/g in C respectively, after 1, 7 and 30 d of ripening. After 60 d, cell densities of NSLAB were similar (∼106 cfu/g) in C and E cheese. Addition of yeast extract to curd affected neither the electrophoretic patterns of cheese nor its water-soluble N content during ripening. However, the total free amino acids were significantly higher in E cheese than C cheese throughout ripening, suggesting faster secondary proteolysis in the former cheeses. A 6-member trained descriptive panel evaluated the cheese at 7 months and found that the E cheeses had higher intensities of whey, fruity, sulphur, nutty, sweet and sour flavours, but had lower intensities of brothy flavours as compared to C cheeses. Also, the E cheeses were perceived to be more mature than corresponding C cheese. Results show that addition of yeast extract to cheese curd is a promising method of enhancing flavour development in ripened cheeses.

Gene-specific probes were used to assess the expression patterns of four different phenylalanine ammonia-lyase (pal) genes in infected or elicitor-treated leaves and suspension-cultured cells of barley. Genes corresponding to hpal2, hpal3, hpal4, and hpal6 were all induced by mercuric chloride and fungal infection by Bipolaris sorokiniana Sacc. (Shoem.) in barley (Hordeum vulgare L. cv. Pokko) leaves, but with considerable variation in their expression level and timing. The expression patterns of hpal2 and hpal6 were similar, both showing a rapid, strong induction after treatment with mercuric chloride and a slower induction after fungal inoculation, whereas the more divergent hpal3 was induced at a later time and at a lower level after both treatments. Hpal4 was expressed with timing like that of hpal2 and hpal6 in infected or mercuric chloride-treated leaves but its expression was much weaker. Hpal2 and hpal4 were induced in elicitor-treated, suspension-cultured barley cells, whereas the expression of hpal3 was nearly undetectable, and hpal6 was strongly and constitutively present. All pal genes except hpal4 were developmentally regulated, but differentially expressed in various barley tissues. The results suggest that the four pal genes studied here might be responsible for the activation of different branches in the phenylpropanoid biosynthesis of barley.