Effect of freeze drying on alpha glucosidase, angiotensin (ACE) inhibition, and nutritional properties of Lactococcus lactis-fermented guava fruit powder

To investigate the biological activities and physicochemical properties of Lactococcus lactis-fermented guava (Psidium guajava, Punjab pink var) pulp powders prepared using freeze drying (FD).

Proximate composition of these powders was determined using standard protocols by the DPPH radical scavenging assay. The powder samples were examined for biological activities—alpha glucosidase and angiotensin inhibition. SEM was used to determine morphology of FD powders; textural analysis was carried out instrumentally and sensory evaluation using 9-point hedonic scale. Microbiological analysis and shelf life (3 months) properties of powder samples were done as per recommended guidelines.

The FD-stabilized fermented guava powders consisted of protein (5.8 ± 0.01 mg/100 g), fat (3.9 ± 0.04 mg/100 g), moisture (4.82 ± 0.003 g water/g d.b), and carbohydrates (30.8 ± 0.92 mg/100 g). Vitamin C (119.2 ± 8.78 mg/100 g), lycopene (703 ± 6.77 mg/GAE/g), and antioxidant activity (81.2% ± 3.30). Alpha glucosidase activity and angiotensin inhibitory activities were (IC₅₀) 3.40 ± 0.08 and 2.52 ± 0.31 µg/mL, respectively, did not differ significantly (p > 0.05) than those observed in fermented pulp. Significant (p < 0.05) reduction of these values occurred in hot air-dried (HD) powders. SEM indicated uniformly distributed pores in FD-stabilized powders. Textural analysis of powders revealed these to be free flowing with low cohesive index (CI: 4.33) and caking tendency (mean caking strength: 177.37). FD guava powders that received high sensory scores were shelf stable at 28 °C for up to 3 months with insignificant (p > 0.05) changes in biological activities. The APC < 1 CFU and absence of molds and yeasts, coliforms, and Staphylococcus aureus in guava powders indicated microbiological safety.

The physicochemical properties and biological activities of L. lactis-fermented guava pulps can be effectively stabilized as a valuable food ingredient using FD for developing a functional food ingredient and a safe, healthy choice of nutrition.