The Effects of Stress Factors on the Growth of Spoilage Yeasts Isolated From Apple‐Related Environments in Apple Juice

Abstract

AbstractThis study aimed to evaluate the effects of temperature, pH, sugar content and antimicrobial components on the growth of 11 yeast isolates in apple juice (12 °Brix, pH 4.0). The results showed that reduction of the storage temperature to 4C could achieve a complete inhibition of test strains, and the temperature required to kill all the initial yeast inoculum (103 cfu/mL) within 20 min ranged from 46 to 55C, depending on the isolate. However, high sugar content enabled test strains to survive in what would have been a lethal treatment. A pH value below 2.0 had a significant inhibitory effect on the growth of test strains. Increasing the sugar content of apple juice was not enough to completely avoid the spoilage caused by the test strains, especially Zygosaccharomyces rouxii. Addition of antimicrobial components (4.0 mM sorbic acid, 1.5 mM cinnamic acid, 20 mM vanillin, 10 mM ferulic acid or 12 mM p‐coumaric acid) was an applicable strategy to prevent the spoilage in apple juice spawned by the test strains.Practical ApplicationsWith the rapid improvement of living standards, there has been a considerable increase in the demand for better quality apple juice. Quality deterioration is a frequently reported problem in apple juice industry, which mainly resulted from microbial contamination, especially osmotolerant yeasts, that alters the original flavor by the production of new odor‐active metabolites. Therefore, development of effective strategy to prevent the spoilage is an important issue. Stress factors including temperature, pH, sugar content and antimicrobial components are all used to inhibit yeast species and other microorganisms in food. Study of the effects of these factors on the growth of yeasts is advantageous to extend the microbial stability of apple juice during storage. The results show that addition of antimicrobial components, applicable to apple juice industry, is sufficient to extend the shelf life of apple juice for more than 50 days.