Guava (Psidium guajava L.) is an exotic fruit with a unique tropical flavor. It is considered to be an excellent source of nutrients, phytochemicals and antioxidants, especially ascorbic acid. The high perishability of the fresh fruit limits its marketability within the US. Guava puree is a commonly processed fruit product which can be pasteurized to extend its shelf life, but pasteurization has negative effects on sensory and nutritional quality. A non-thermal process is desirable to protect the fresh flavor and nutritional value of guava puree, which is used as base for production of guava beverages and other food products.
The objective of this research was to evaluate a new technology, Non-Thermal Dense Phase Carbon Dioxide Pasteurization (DP-CO₂), for the processing of guava puree. The hypothesis was that the use of (DP-CO₂), would minimize or prevent undesirable changes in phytochemical composition compared to traditional heat pasteurization. In order to validate this hypothesis, measurement and comparison of the chemical composition of the guava puree subjected to both treatments and an untreated guava puree (freshly-thawed control) were conducted.
To facilitate processing the puree through the DP-CO2 equipment, viscosity of the puree was modified. A commercially available enzyme, Bioguavase was used for this purpose. Samples were treated with the enzyme and evaluated for changes in viscosity at three hour intervals for up to 12 hours of reaction time. The enzyme treatment increased juice yield, produce a puree of lower viscosity, decreased the antioxidant capacity, and reduced the total phenolic content of the product. The enzyme treatment also decreased the pH of the juice due to the release of galacturonic acid from the pectin hydrolysis and increased the total soluble solids content. Three hours of reaction time and 600 ppm of enzyme concentration were adequate to produce a clarified juice.
Microbial reduction was quantified as a function of pressure and residence time using 8% CO₂ level and a temperature of 35 oC. Optimum DP-CO₂ treatment conditions for microbial inactivation were determined to be 34.5 MPa for 6.9 min and 8% CO₂ at 35 oC. Quality attributes, including pH, oBrix, % titratable acidity (%TA) and color of DP-CO₂ treated, freshly thawed and heat pasteurized (90oC for 60 s) guava puree were measured and compared throughout refrigerated storage (4oC for 14 weeks). DP-CO₂ treatment did not cause a change in pH or oBrix but increased the titratable acidity and viscosity of the product. Pectinesterase enzyme (PE) was partially inactivated after DP-CO₂ processing. DP-CO₂ treated guava puree retained organic acids contents similar to fresh guava puree and served to protect polyphenolic and antioxidant levels throughout processing and storage. DP-CO₂ delayed the degradation of Vitamin C content during storage.
Flavor and aroma compounds of guava puree were identified. Flavor profiles showed that heat treated guava puree had less aroma active compounds than DP-CO₂ treated guava puree. DP-CO₂ decreased the total area of volatile compounds when compared to fresh and pasteurized, but differences in volatile composition were found for the three samples.
DP-CO₂ is an effective alternative to heat pasteurization of guava puree. It reduces microbiological load, extends the shelf life, and preserves important sensory and nutritional characteristics of the puree.