Modeling of pre-treatment protocols for frozen pineapple slices

All washing was performed in ethanol-rinsed, dried and UVirradiated plastic zip-lock bags after which the food matrix and buffer wash was gently agitated at 80 rpm for approximately 20 min and immediately passed through a 40 μm nylon cell strainer (BD Falcon; Becton Dickinson Biosciences, Bedford, MA) to remove large food particles. The food washes typically had a slightly green hue.

Freezing is one of the best and oldest methods for long term preservation of fruits and vegetables.Fresh fruits and vegetables undergo various physico-chemical and biological changes after harvest resulting in deterioration and reduction in various quality attributes. Freezing process considerably reduces the rate of the deleterious oxidative and enzymatic reactions and also inhibits the growth of microorganisms resulting in a much safer product (Bremer & Ridley.

Fruits

Fully mature pineapple fruits (cv. Giant Kew) were procuredfrom the local Mysore (India) market for this study. The fruits were sorted and graded on the basis of size, shape and maturity and those with visible infections and mechanical injuries were rejected.The selected fruits (80 kg) were subjected to surface sanitation wash in chlorinated water (0.01%). The washed fruits were peeled and cut into 12.0 mm thick slices (40 kg) for the pretreatment andfreezing..

Experimental design

Response surface methodology was used for designing theexperiment (Khuri & Cornell, 1987) to study the effect of pretreatment protocols and freezing on the quality of frozen pineapple slices. A Central Composite Rotatable Design (CCRD) was used taking 3 variables at 5 levels each with 6 central points.

Texture analysis

Textural analysis of pineapple slices was performed by determining the firmness using a texture analyzer (TAHDi, Stable Microsystems, London, UK) loaded with Texture Expert software (Version 1.22; Stable Microsystems, London, UK). The firmness was measured by cutting the pineapple slices (12.0 mm) at the centerwith a Warner Bratzler Blade using a test speed of 0.5 mm s1

In addition, calcium chloride treatment was found to have a greater effect on sensory acceptability compared to sugar and ascorbic acid treatments. The optimised levels of variables can be used in the commercial production of frozen pineapple slices to ensure optimal physicochemical properties of the product during long-term frozen storage.

The variables used in the study viz. blanching mediumconcentration, calcium chloride and ascorbic acid pretreatmentwere found to significantly effect sensory attributes, colour (L*),rip loss and textural properties of the frozen pineapple slices.Polynomial models were found to fit the experimental data well with high R2 values, thus, confirming the adequacy of the model for the responses (i.e. syneresis, sensory, colour and textural attributes) studied. The calcium chloride pretreatment prior to freezing was found more effective than sugar blanching in minimizing driplosses and maintaining texture of frozen and thawed pineapple slices.