Title : Physicochemical and microbiological stability of yogurt fortified with polysaccharides from Pleurotus ostreatus by-products
Abstract:
The global edible mushroom market has expanded significantly in the last years, with production expected to exceed 20 million tons annually by 2026. Among the most widely cultivated species is the Pleurotus ostreatus. During the commercialization of fruiting bodies, considerable quantities of by-products are produced, mainly consisting of Spent Mushroom Substrate (SMS) and stems. Both SMS and stems contain a range of valuable compounds, including polysaccharides, crude protein, trace elements, and vitamins.
The objective of this study framed into BIOFOOD project was to evaluate the impact of incorporating polysaccharide extracts derived from Pleurotus ostreatus by-products (stems and SMS at 3% and 6% on the physicochemical, technological, and microbiological quality of fermented yogurt during a 15-day refrigerated storage period (T0 = 0 days, T1 = 5 days, T2 = 10 days and T3 = 15 days). The research focused on determining how these bioactive compounds alter the dairy matrix in terms of pH, titratable acidity, Lactic Acid Bacteria (LAB) viability, susceptibility to syneresis, and colour stability using the CIELab system.
The results revealed a critical divergence in chemical behaviour depending on the type of extract used. The addition of SMS significantly increased the pH of the final product, reaching a value of 4.87 in the 6% dose, which reduced the titratable acidity to 1.30% compared to the control (pH 3.70; acidity 1.60%). Conversely, P. ostreatus stems extracts maintained a more physiological and stable acidity profile at both 3 and 6% during storage from T0 (pH 3.84 and 3.92, respectively) to T3 (pH 3.81 and 3.91, respectively), similar to the control (T0 = 3.78 and T3 = 3.70). From a microbiological perspective, P. ostreatus stems extracts, when added at 6%, achieved a 2-log increase (1.5x109 CFU/g) at T0 compared to the control (3.4x107 CFU/g), suggesting potential prebiotic behaviour. However, a drastic loss of viability was observed toward the end of the study (T3 = 8.7x104 CFU/g), comparable to the control (T3 = 6.1x104 CFU/g).
Regarding technological performance, the 6% stems extract exhibited excellent stabilizing capacity with a lower syneresis at T3 (30.40%) compared to the control (54.28%). In marked contrast, the 6% SMS extract caused severe destabilization of the casein matrix, resulting in a syneresis of 82.47% at T3; this phenomenon is attributed to the increase in pH above the isoelectric point of the dairy proteins. Finally, color analysis showed that SMS generated the most profound optical alterations, with a drastic reduction in lightness (L*) and an increase in yellow saturation (b*), reaching a total color difference (ΔE) of 43.97 relative to the control. On the other hand, the lower ΔE was noted at 3% of P. ostreatus (10.35) and 6% (15.02). It is concluded that P. ostreatus stems extracts possess greater aptitude for integration as functional ingredients, as they improve initial probiotic bacteria and physical stability without compromising the acid equilibrium. The project leading to this report has received funding from European Regional Development Fund (ERDF), granted to the Autonomous Community of La Rioja within the ERDF Operational Programs 2021–2027 (project number: CT24_05).
Keywords: Pleurotus Ostreatus, Mushroom By-Products, Yogurt, Lactic Acid Bacteria, Syneresis, CIELab Color, Physicochemical Stability.
