Determination of a thermal process schedule for guava (Psidium guajava Linn.)

Abstract

SummaryA thermal process schedule for guava canned in syrup has been evolved on the basis of inactivation of pectinesterase (PE) which was found to be more heat resistant than peroxidase. The values for thermal inactivation and thermal resistance of PE in syrup homogenate containing guava pulp and sugar syrup in the ratio of 11:6 and total soluble solids content of 20% at pH 4.0 were respectively. The F value of 1 was equivalent to 1.69 D. In commercial canning, a 2.5 D process is recommended which ensures a microbiologically safe and organoleptically acceptable product.Process time was calculated both by graphical and formula methods. Calculation by the formula method using slopes of heating and cooling curves plotted on semilog paper by least squares analysis, and fh/U:g tables for actual values of jc gave process times very close to those obtained by the graphical method. The process times required at different initial and processing temperatures are given.To minimize viscosity increase in the covering syrup during storage, firming of guava in 1% calcium chloride solutions for 30 min prior to canning is suggested. In addition, use of covering syrup containing 0.125% ascorbic acid with or without citric acid (0.06%) yields a product of good colour, texture and flavour.