Optimization of Thermoultrasound Process of a Soursop (Annona muricata) Nectar and Its Comparison with Pasteurization on Physicochemical Properties and In Vitro Bioaccessibility of Antioxidants

Abstract

Research background. Soursop nectar contains antioxidants and for its conservation the pasteurization is applied. However, this technology decreases its physicochemical properties and bioactive compounds, hence, an alternative is the thermoultrasound which could counter these effects. Therefore, the thermoultrasonicated nectar was compared to a pasteurized one and the in vitro bioaccessibility of antioxidants was estimated. Experimental approach. The soursop nectar (25 %) was elaborated and the response surface methodology was used. The thermoultrasound (TUS) (75-90 % amplitude; 3.15-15 min) was applied, and 2 % stevia and 6 % of agave inulin were added as sweeteners. The microbiological, physicochemical, enzymatic and antioxidant properties were analyzed. The nectar was prepared again and control, optimized TUS and pasteurized were compared. In addition to the aforementioned determinations, microstructure, total dietary fiber (TDF) and in vitro bioaccessibility of antioxidants were performed. Results and conclusions. The response variables that fit the mathematical model were L*, b*, Chroma (C*), total phenolic content (TPC), antioxidant activity by ABTS•+, DPPH• and ferric reducing antioxidant power (FRAP). The L* and DPPH• were influenced by quadratic time and TPC by time (p<0.0001). The optimal TUS condition was 82 % amplitude at 9.15 min and the responses variables were L*, b* and C* (45.48, 3.55 and 3.62, respectively), TPC (38.40 mg GAE/100 mL), ABTS•+ (31.28 μmol TE/100 mL), DPPH• (124.22 μmol TE/100 mL) and FRAP (3.06 μmol Fe (II)/100 mL). In comparison with the pasteurized sample, optimized TUS had high value of TDF (3.53%), L* (45.56) h° (-56.49), TPC (26.63 mg GAE/100 mL), ABTS•+ and DPPH• (22.03 and 129.22 μmol TE/100 mL, respectively), FRAP (3.10 μmol Fe (II)/100 mL) and low pectin methylesterase activity (0.28 PMEU/mL). For in vitro bioaccessibility, the optimized TUS nectar showed high absorption of TPC (15.26 GAE/100 mL) and high values in the antioxidant activity by ABTS (34.92 μmol TE/100 mL) and FRAP (7.88 μmol Fe (II)/100 mL). Novelty and scientific contribution. The thermoultrasound improves the physicochemical properties and in vitro bioaccessibility of antioxidants soursop nectar. On the other hand, as an alternative, this beverage provides low-calorie with prebiotic properties for the benefit of consumer health.