Predictive Evaluation of Microbiological Stability of Soft Drinks with Lycium barbarum L. Stored at Temperature Shifts

Abstract

Lycium barbarum L., used in Chinese traditional medicine for centuries, has gained popularity in Europe in the last decade because of its health-promoting properties assigned to phenolic compounds and antioxidant activity. Goji fruits and extracts are often used as ingredients in popular homemade milk cocktails. Within this study, the microbiological stability of the milkshake, with the addition of berries from NingXia Province and their extract, was evaluated using the ComBase® prognostic model. The extraction of dry berries in water at 70 °C for 72 h produced an extract showing radical inhibition of 64.9% and a total phenol content of 63.6 mg g−1. The phenolic compounds with the highest concentrations were in turn: 3-hydroxybenzoic acid, gallic acid, procyanidin B2, and catechin. The milkshake inoculated with the reference B. subtilis was a model for the study of its microbiological stability. Using ComBase®, a microbiological response to the delayed cooling of goji berry extract and the milkshake with the addition of goji berries was predicted and the model’s accuracy assessed. The best-performing models were constructed for extract (Bias factor Bf 1.33, Accuracy factor Af 3.43) and milkshake (Bf 1.29, Af 1.65) in a profile simulating delayed refrigeration (22.5 °C–9 °C–23 °C). Despite discrepancies between predicted and observed bacterial growth due to the antimicrobial effect of the derivatives of goji berries, the models were validated as „overpredict”, i.e., „fail safe”, and may be used to prognose the stability of these products in the given temperature profile.