Effect of Novel Processing Techniques on Texture Softening and β-Carotene Content of Thermally Processed Carrots

Abstract

Effect of novel processing methods was evaluated on product texture and β-carotene content of carrots following acidification to reduce pH from 6.0 to 4.4. Thermal treatments under Conventional (CH-T) and Ohmic heating (OH-T) conditions at 87, 92, and 97 °C, individually and/or in combination with high-pressure processing (HP-T; 400–600 MPa/40–60 °C), were given up to 90 min. A fractional conversion model was used to compute texture softening rate constant, k, and activation energy, Ea. Acid-infused carrot samples had lower k values than the control, implying a better texture retention in acidified products. In order to explore this further, acid-infused and control samples were subjected to selected processing methods for 0, 7, and 25 min representing minimal, optimum, and over-processing conditions, respectively. Texture value, pectin depolymerization by β-elimination, demethoxylation, cell microstructure modification, and β-carotene content were evaluated. Results showed that acid-infused samples retained significantly (p ≤ 0.05) better texture than the untreated ones. Pectin depolymerization by β-elimination was greater (p ≤ 0.05) in control samples than acid-infused samples. In contrast, pectin depolymerization by demethoxylation showed no such differences (p > 0.05) with acid-infused samples. This indicates that pectin degradation was more dominated by β-elimination than demethoxylation, and these results concurred with the cell microstructure observations of processed carrots. Thermal and HP-T processing after acid infusion reduced the β-carotene content of carrots more than in control. However, mild heat treatment of carrots at 97 °C under CH-T and OH-T enhanced the β-carotene levels to higher than in raw control carrot samples.