Effects of pectinase enzyme and mannoproteins on the quality of guava (Psidium guajava L.) nectar juices

Guava (Psidium guajava L.) juice is mostly cloudy due to colloidal suspension after extraction, which is a challenge to the industry as consumers prefer clear juice. The objective of this study was to investigate the effects of mannoproteins and pectinase enzyme (rapidase^®) treatments on clarification nectar blends produced from guava juice. Prior to pasteurisation at 90°C and packaging, guava juice was treated with varying concentrations and combinations of pectinase enzyme (E) and mannoproteins (M): i) 100% M; ii) 100% E; iii) 50% E:50% M; iv) 70% E:30% M; v) 30% E:70% M; and vi) non-treated guava juice sample (control). All samples were stored for 7 days at 4°C, and quality attributes including colour, total soluble solids, organic acids, phenolic compounds, flavanols, and flavonoids were quantified at regular intervals. Based on the absorbance readings, the guava nectar sample treated with 50% E:50% M showed the least (p≤0.05) at 420, 520 and 620 nm wavelengths. Four phenolic compounds were detected in the guava nectar, including gallic acid, isoquercitrin, epicatechin-3-gallate (ECG) and epigallocatechin-3-gallate. At the end of day 7, the guava nectar sample treated with 50%E:50%M had the highest garlic acid and ECG concentration (p≤0.05). The use of pectinases in combination with mannoproteins as an aid for clarification of guava juice was effective and resulted in a clear juice with a brighter purple to red colour.