Yoghurts and yoghurt products continue to increase in popularity, and the growth in consumer demand is partly linked to the development of novel formulations and product lines. Yoghurt is a nutritious commodity, and for this trend to continue, further innovations in yoghurt products are required.

"Fresh-like" foods with minimal processing are popular with consumers, and one option is to formulate yoghurt products that appeal to this demand. Although yoghurt is relatively unprocessed, fruit-flavoured yoghurts contain heat-treated fruit. This processing is required to inhibit and destroy yeasts such as Candida famata and Kluyveromyces marxianus, which can grow at refrigeration temperatures. These spoilage bacteria and fungi in fruit can limit the production of minimally processed fruit yoghurt unless measures are taken to inhibit their growth.

Natural preservatives derived from food plants and food-grade microbes are of interest for reducing microbial growth in yoghurt containing minimally processed fruit. Vanillin is a phenolic compound used for flavouring, which has broad-spectrum antimicrobial properties, particularly against fungi and yeasts. Nisin is a food-grade bacteriocin that inhibits most Gram-positive bacteria. Cranberries contain various phenolic acids, flavonoids and uncharacterized polymers, which actively affect the adherence of pathogenic bacteria such as Escherichia coli.

A study by Penney et al.¹ investigated the efficacy of vanillin, nisin and fresh cranberries to control microbial spoilage of yoghurt containing minimally processed wild blueberries. The effects of vanillin on the viability of acid-adapted E. coli in yoghurt were also evaluated. Nisin was ineffective in preventing spoilage, while fresh cranberries extended shelf life by one week. However, vanillin suppressed the growth of spoilage microbes, and it is suggested that such phytopreservatives could have potential as natural antimicrobials in minimally processed fruit yoghurt.
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¹ Penney, V; Henderson, G; Blum, C; Johnson-Green, P (2004). The potential of phytopreservatives and nisin to control microbial spoilage of minimally processed fruit yogurts. Innovative Food Science and Emerging Technologies 5 (3) 369-375.

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