Assessment of Probiotic Properties and Consumer Acceptability of Yogurt Made from Commercial Milk using Bacterial Isolates from NONO
Abstract
Nono is a traditionally fermented milk product commonly consumed in parts of Nigeria. It undergoes spontaneous fermentation by lactic acid bacteria (LAB), conferring potential probiotic properties. This study isolated and identified LAB from Nono and assessed their suitability as novel starter cultures for yogurt production using commercial milk. Three LAB isolates were obtained from Nono samples on selective media. They were Gram-positive rods, catalase-negative, with ability to ferment various sugars. The isolate with the greatest antimicrobial activity against Escherichia coli and Staphylococcus aureus was molecularly identified as Lactobacillus fermentum. Set-type yogurt was produced at laboratory scale by inoculating reconstituted commercial milk (14% total solids) with 2% of commercial starter culture (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus); 2% L. fermentum; and 1% each of commercial starter and L. fermentum. The probiotic, physicochemical, sensory and storage properties were analyzed. L. fermentum-containing yogurts had lower pH and higher titratable acidity than the control yogurt. Proximate composition was similar across samples. Sensory evaluation showed comparable consumer acceptability, with slight preference for the control sample. Yogurt with L. fermentum maintained higher viable LAB during storage at refrigeration temperature for 28 days. The findings demonstrate the potential for using LAB isolates from traditionally fermented foods like Nono as novel starter cultures in yogurt manufacture. This can promote product diversification and valorization of indigenous fermentation practices.
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Introduction
Probiotics are live microbial food supplements that confer health benefits on the host when consumed in adequate amounts (Hill et al., 2014). Fermented foods are regarded as important probiotic carriers, with yogurt being the foremost dairy product acclaimed for its probiotic properties (Granato et al., 2010). Yogurt popularity has surged in recent years due to associated nutritional and therapeutic advantages (Hekmat and Reid, 2006). Its industrial production involves fermentation of milk by starter cultures consisting principally of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus (Sfakianakis and Tzia, 2014). These bacteria impart yogurt’s characteristic texture, flavor and acidity by producing lactic acid from lactose fermentation (Gonzalez-Gonzalez et al., 2011).
Besides the traditional yogurt starters, other lactic acid bacteria (LAB) can also be incorporated as adjunct cultures to diversify yogurt products. For instance, Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium spp. are often used as probiotic enrichments in commercial yogurts to enhance health attributes (Donkor et al., 2007). A growing consumer preference for natural, minimally processed foods has fueled interest in using novel LAB strains isolated from traditional fermented products as starter cultures (Bourdichon et al., 2012). Such strains possess inherent robustness and diverse enzymatic activities tailored by years of adaptation to their natural niches. This can potentially improve yogurt functionality, quality and uniqueness (Leroy and De Vuyst, 2004).
Conclusion
The findings of this study demonstrate the potential of isolates obtained from traditionally fermented Nono to be developed as novel functional starter cultures for yogurt production. The Lactobacillus fermentum isolate showed good survival under conditions simulating the gastrointestinal tract, indicating its robust probiotic properties. Incorporation of this isolate into yogurt fermentation enhanced the physicochemical attributes by improving acidification compared to the control. Sensory evaluation revealed comparable consumer acceptability among yogurts produced with different starter combinations. Moreover, viable counts of probiotic bacteria were maintained at a higher level during refrigeration storage of yogurt with added L. fermentum. Overall, the results suggest that LAB from indigenous fermented foods like Nono have the capacity to be developed as adjunct starter cultures for diverse probiotic dairy products. This offers opportunities to valorize traditional fermentation practices and promote product innovation through strain diversification. Further research could optimize the Nono isolate's application in diverse dairy and non-dairy probiotic foods.