Effect of semi-defatted walnut and pumpkin flour fortification on the physicochemical, microbiological, and sensory properties of yogurt

Abstract

Yogurt is a nutritionally rich dairy product that plays a key role in human health. With growing consumer demand for functional foods, the fortification of yogurt with nutrient-dense ingredients has gained interest. In this study, pasteurized cow's milk was inoculated with Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus and Lactobacillus rhamnosus, and fortified with walnut and pumpkin semi-defatted flours to evaluate the effects on physicochemical, microbiological, and sensory properties over 7 days of storage. Walnut and pumpkin flours, oil-extraction by-products, are rich in nutrients and support circular economy principles. Fortification significantly influenced pH, titratable acidity, dry matter, fat, protein content, water-holding capacity, and total phenolic concentration. The addition of walnut flour resulted in a more pronounced decrease in pH and increased acidity due to enhanced lactic acid bacterial activity, whereas pumpkin flour-fortified yogurts exhibited higher protein content. Fortification increased dry matter and fat content. Total phenolic concentration significantly increased in fortified samples, with walnut flour showing a greater enhancement than pumpkin flour. Sensory evaluation confirmed that fortification improved yogurt acceptability without negatively impacting texture or flavour. These findings highlight the potential of walnut and pumpkin semi-defatted flour as functional ingredients in yogurt production, promoting sustainability and adding value to agro-industrial by-products.