Fortification of low-fat yogurt with melloco flour (Ullucus tuberosus): Physicochemical and rheological effects

Yogurt is a fermented milk product containing Lactic Acid Bacteria (BAL) (Lactobacillus bulgaricus and Streptococcus thermophilus). Although the application of additives is not mandatory, the use of gums or dairy extenders have been studied to establish the effect on the product. Among the additives most used in yogurt, production is focalized on natural or artificial sweeteners, stabilizing agents, flavors and colorants. Nowadays, consumers are looking for products that seem less artificial and more natural. In this sense, melloco, an Andean crop that, thanks to its mucilaginous content, could become an excellent additive that provides stability and viscosity. This study aimed to evaluate the effect of melloco flour (Ullucus tuberorus) yellow variety (INIAP-Quillu) on low-fat yogurt's quality properties. In this study, semi-skimmed milk (2% fat) was supplemented with 0.9% (w / v) of melloco flour, fermented and stored at 4°C for 20 days. Sensory attributes such as color, texture, taste, smell and overall acceptability were evaluated; the proximal analysis was performed using official methods of the Association of Official Analytical Chemists (AOAC). The physical and rheological properties and microbiological analysis were evaluated during 20 days of refrigerated storage. The use of melloco flour to enrich the reduced-fat yogurt improved acid production during fermentation. The average pH of the samples decreased from 4.8 to 4.18 after 20 days of storage. The color parameters did not differ significantly in all samples and remained constant during storage. The viscosity showed a rheological behavior of the pseudoplastic fluid. This study evidenced that the acid production in the yogurt enriched with melloco flour was higher during fermentation than the control sample, the typical end-point of pH (4.5) was reached by enriched yogurt in 5.5 hours compared to 7 hours for control. Sensory attributes also allowed establishing that the sample with 0.9% of flour presents the best overall acceptability. In general, the results suggest that melloco flour can be considered as good gelling and nutritional agent for the production of yogurt. Key words: enriched, fermentation, Melloco, microbial growth, yogurt, physicochemical properties, rheology, sensorial properties