PurposeThe purpose of this study was to characterise the physiochemical properties of selected exotic seasonal tropical fruits available in Singapore.Design/methodology/approachA total of 11 seasonal tropical fruits including cempedak, chiku, custard apple, jackfruit, longkong, mangosteen, red jambu, pearl jambu, rambutan, salak and starfruit were analyzed for their sugars, organic acids and free phenolic acids composition using liquid chromatographic methods. Total phenolic content (free and bound), total soluble solids and pH were determined using Folin‐Ciocalteu method, refractometer and pH meter, respectively.FindingsFructose, glucose and sucrose were the main sugars in all the fruits. Cempedak had the highest sucrose concentration, while custard apple had the highest content of fructose and glucose. Malic and citric acids were the major organic acids in most of the fruits, except for pearl jambu and red jambu where succinic acid was the dominant acid. The total phenolic content varied from 122.94 to 712.20 mg gallic acid equivalent (GAE)/kg fresh weight (FW). Ferulic (0.631 mg/kg) and sinapic acids (1.506 mg/kg) were the predominant free phenolic acids in custard apple, while caffeic acid was the main free phenolic acid in jackfruit, salak and starfruit.Originality/valueThe paper demonstrates that the physiochemical characteristics of the 11 tropical fruits varied markedly, which is responsible for the differential flavour and stability. The findings are useful for epidemiological research and predicting the degree of ripeness, stability and post‐harvest processing required for these fruits.

PurposeThere is a need to improve stability of lactic acid bacteria (LAB) and probiotics in fermented milks especially at elevated temperatures. The purpose of this paper is to evaluate the impact of yeast Williopsis saturnus var. saturnus on stability of LAB and probiotic Lactobacillus rhamnosus in fermented milks.Design/methodology/approachFermented milks were made from reconstituted whole milk with different milk solids contents. The milk was fermented with L. rhamnosus DR20 with and without yoghurt cultures. The treatment had yeast added, whereas the control did not. Fermented milks were incubated at different temperatures and samples were taken regularly for microbial count determination.FindingsThe effect of the yeast on stability of L. bulgaricus and L. rhamnosus varied with temperatures: no effect at 4 and 40 ○C, increasing effects from 10 to 30 ○C with enhanced lactobacilli survival by 102 to 107‐fold. The yeast enhanced L. bulgaricus and L. rhamnosus stability by approximately 106 to 107‐fold in fermented milks with 5 per cent w/v and 20 per cent w/v milk solids at 30 ○C.Research limitations/implicationsUse of live yeast has limitations. The yeast must not ferment lactose and galactose, and fermentable sugars cannot be used as sweeteners to avoid yeast growth. Further understanding of the interaction between yeast and LAB may eliminate the need to add viable yeast.Originality/valueUse of yeast to enhance stability of LAB and probiotics is a novel concept. Addition of selected yeast could be an effective means of enhancing stability of LAB and probiotics in fermented milks to extend shelf‐life and to retain nutritional value.

SummaryThis study investigated the effect of initial sugar concentrations (°Brix of 17, 23 and 30) on mango wine composition fermented by Saccharomyces cerevisiae MERIT.ferm. It was found that growth rate and maximum cell population were inversely correlated with initial sugar levels with the fastest growth rate and largest cell population in the low sugar fermentation. However, the cell population in the low and medium sugar fermentation declined significantly (from 8.7 and 8.2 log to 2 and 2.8 log, respectively) relative to the high sugar fermentation in which cell populations remained stable upon reaching the stationary phase (7.7 log). Glycerol production increased with increasing sugar content in low (13.4 g L respectively) sugar fermentations. Furthermore, volatiles especially terpene hydrocarbons (a-caryophyllene was released) present in mango juice were significantly metabolised after fermentation, while numerous new volatile compounds (such as isobutyl alcohol, isoamyl alcohol, ethyl and acetate esters) were produced. Some terpene alcohols were released and converted into corresponding acetyl esters. This may indicate that the mango wines fermented with different levels of sugars would have different flavour aromas.

This study demonstrates the potential of utilizing specific yeast species as starter or adjunct cultures to simultaneously improve the growth of fastidious bifidobacteria and modulate the organoleptic properties of fermented food products.