Purpose The purpose of this paper is to investigate in situ production of aroma‐active esters in dairy foods so as to improve flavour and to produce fruity flavour concentrate. Design/methodology/approach Lipase, ethanol or bacterial cultures are added to dairy media (milk, cream or cheese) and incubated for a period of time (from hours to months). Samples are then taken and analysed for aroma‐active esters using gas chromatography (GC) or gas chromatography‐mass spectrometry (GC‐MS). Findings Analyses of samples show that significant levels of ethyl esters of fatty acids are produced in milk, cream, enzyme‐modified cheese and natural cheese. All the dairy foods possess an intense pleasant fruity aroma. Originality/value This is a natural way to generate fruity flavours in dairy foods to enhance flavour and thus, consumer acceptance. The fruity flavour concentrate can also be used as a flavouring ingredient in dairy and non‐dairy food applications. Natural pure esters may also be extracted, separated and concentrated for wider flavour and fragrance applications. This approach may provide a cost‐effective solution to the increasing surplus of milk fat.
The fermentation products from 10 strains of propionibacteria accounted for only 72% (average value) of the lactose carbon utilized. The balance of the carbon was accounted for by the production of a polysaccharide containing methylpentose (the major component), glucose, and galactose. The presence of methylpentose explained the low ratios of propionate to acetate (<2:1).
The influence of reduced water activity (aw) on lactose metabolism by Lactococcus lactis subsp. cremoris 2254 and 2272 was studied at different pH values. In control incubations (aw, 0.99) with nongrowing cells in pH-controlled phosphate buffer, the levels of carbon recovered as L-(+)-lactate were 92% at pH 6.1 and 5.3 and 78% at pH 4.5. However, the levels of recovery decreased to approximately 50% at all pH values tested when the aw was 0.88 (with glycerol as the humectant). When growing cells in broth controlled at pH 6.3 were used, a reduction in the aw from 0.99 to 0.96 resulted in a decrease in the level of lactose carbon recovered as L-(+)-lactate from 100 to 71%. Low levels of L-(+)-lactate carbon recovery (<50%) were also observed with cells resuspended in pH-uncontrolled reconstituted skim milk at aw values of 0.99 and 0. 87 and in young cheese curds. The missing lactose carbon could not be accounted for by acetate, ethanol, formate, acetaldehyde, or pyruvate. Attempts were made to determine where the missing lactose carbon was diverted to under the stress conditions used. Some of the missing lactose carbon was recovered as galactose (0.1 to 2.5 mM) in culture supernatants. Decreasing either the aw or the pH resulted in increased galactose accumulation by nongrowing cells; adjusting both environmental factors together potentiated the effect. The sensitivities of the two lactococcal strains tested were different; strain 2272 was more prone to accumulate galactose under stress conditions. A methyl pentose(s) and additional galactose were found in acid-hydrolyzed supernatants from cultures containing both growing and nongrowing cells, indicating that a saccharide(s) rich in these components was formed by lactococci under low-aw and low-pH stress conditions.
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