Physicochemical stability of whey-based beverages formulated with Red Pitahaya (Hylocereus costaricensis) and Cape Gooseberry (Physalis peruviana) during refrigerated storage

Whey is a by-product of the cheese industry that is often underutilized despite its nutritional value and potential for the development of functional beverages. The incorporation of fruit pulps rich in natural pigments and bioactive compounds may improve the physicochemical and sensory characteristics of whey-based beverages. Therefore, the aim of this study was to evaluate the physicochemical stability of beverages formulated with hydrolyzed whey and pulps of red pitahaya (Hylocereus costaricensis) and cape gooseberry (Physalis peruviana) during refrigerated storage. Five formulations were prepared using a whey-to-pulp ratio of 80:20, varying the proportions of pitahaya and cape gooseberry. The beverages were evaluated on days 1, 7, and 14 for pH, titratable acidity, total soluble solids, color parameters (L*, a*, b*), viscosity, and betalain content.

During storage, pH values remained between 3.95 and 4.15, while titratable acidity increased from initial values ranging from 0.48 to 0.79% to 0.68-1.23% on day 14. Total soluble solids ranged from 11.33 to 25.42^° Brix, depending on the formulation. Colorimetric analysis showed that beverages containing higher proportions of pitahaya exhibited positive a* values and negative or low b* values, corresponding to characteristic red-violet hues, whereas the formulation without pitahaya showed a predominance of yellow-orange tones. In addition, a progressive decrease in red color intensity (a*) was observed during storage, which was associated with the degradation of betalains present in pitahaya. In this regard, T1 showed the highest initial betalain concentration (60.97 mg/L), which decreased to 28.07 mg/L after 14 days of storage, representing an approximate loss of 54%. Similarly, the other pitahaya-containing formulations exhibited a progressive reduction in betalain content, highlighting the susceptibility of these pigments to degradation during refrigerated storage. In contrast, T5, which did not contain pitahaya, showed no detectable betalains and displayed a greater tendency toward yellow-orange coloration. Viscosity values ranged from 41.60 to 92.47 cP, with significant increases observed in some formulations toward the end of the storage period. These results demonstrate that the proportion of pitahaya and cape gooseberry significantly influences the physicochemical stability, color characteristics, and betalain retention of hydrolyzed whey-based beverages, with betalain stability being a key factor affecting the visual quality and acceptability of the final product.

Keywords: Hydrolyzed Whey, Red Pitahaya, Cape Gooseberry, Betalains, Physicochemical Stability