The progressive shift of consumers to health-oriented digestive products is driving the yogurt market. The global yogurt market is expected to record a compound annual growth rate of 4.5% during the period 2020–2025. Also, the pandemic of COVID-19 had a short-term positive effect on the retail yogurt market. The functional health benefits of yogurt caused in this period the market to have more demand as consumers were followed better diets and focused on their gut health (Mordorintelligence. Com, 2020).
As the yogurt market grows, the production of yogurt with high quality should be considered. In some traditional yogurts such as Greek-style yogurts that are made from whole milk, the milk does not become homogenized because the thin cream layer formation on the top of the product is desired (Chandan, 2017). Although the market demand for yogurt with a cream layer has increased (Das et al. 2019), because of the high cost of full-fat milk, the possibility of producing yogurt with a cream layer in the industry has been limited. Also according to market demand for traditional yogurt, there is the probability of fraud in this kind of product is also possible.
Generally, yogurt is not a very stable product, and its shelf-life is limited to about 3 weeks in cold storage and 2–3 days at room temperature (Lacroix & Lachance, 1990). Moreover, this product is particularly vulnerable to fungal growth due to its pH, water activity, and nutritional profile. Fungal contamination can cause discoloration, off-flavors, and alterations in texture and appearance, leading to loss of quality, waste, and consequently, economic losses. Fungi could tolerate acid, and easily contaminate all stages of yogurt processing (Delavenne et al., 2015).
Research indicated that the most important fungal spoilage generous of yogurt in Iran consists of Aspergillus, Penicillium, Mucor, and Stemphylium. A. terreus is also the most frequent species (45.35%) that caused fungal contamination in yogurt (Moshtaghi et al., 2015). A. terreus is the main fungus that can contaminate stored food products in tropical and subtropical climates, and it is thermophile and the minimum water activity for its growth is reported to be 0.78 at 37°C (Pitt, 2009).
A protective layer on the surface of yogurt with antimicrobial and nutritional properties could limit the penetration of oxygen and spoilage agents and improve the shelf life of the yogurt (Corsetti & Settanni., 2007; Delavenne et al., 2013). In this study, we were inspired by the creamy layer of the traditional yogurt and designed protective edible layers with functional properties to improve the sensory and quality properties of yogurt. The protective layer was prepared based on wheat sourdough, wheat flour, and bovine bone gelatin incorporated with L. plantarum, and their antimicrobial and antifungal properties were assessed in virto. Also, the effect of designed layers on the shelf life, physicochemical, and sensory properties of yogurt samples was evaluated.