Abstract:
The objective of this study was to investigate the effect of honey and pineapple juice on mass transfer, drying kinetics and quality of osmotically dehydrated-air dried beetroot. Initially, beetroot pieces were pre-treated by soaking in a solution containing 1% (w/v) citric acid and calcium chloride at four different levels (0, 0.5, 1.0% and 1.5% w/v). Beetroot pieces treated with the mix solution containing 1% (w/v) calcium chloride had a highest calcium content but not significantly different from those treated with solution containing 1.5% (w/v) calcium chloride (p>0.05). The 1% (w/v) calcium chloride treatment resulted in beetroot pieces with highest hardness. However, this was not significantly different from 0.5 and 1.5% (w/v) calcium chloride treatments (p>0.05). Beetroot pieces were then immersed sequentially in 35 and 45 ºBrix sucrose solution for 6 hours each. At 45º Brix level, an osmotic agent, either 10% and 15% (v/v) honey or pineapple juice was used to partially replace sucrose (H-10, H-15, P-10 and P-15). The treatment without honey and pineapple juice and the treatment with 10% (v/v) invert sugar replacement were set as a control and a reference, respectively. The H-10 and H-15 yielded the highest water loss (WL) and highest solid gain (SG) than other treatments. The osmosed beetroot were then dried in a hot air drier at 60 ºC until a moisture content of about 14% (wb) was obtained. It was found that H-15 exhibited the fastest drying rate followed by H-10, P-15, P-10, reference and control, respectively. Modified Henderson and Pabis model was found to be the best model for describing the drying behavior of all treatments. For dried products, the H-10 and H-15 possessed significantly higher glucose and fructose contents than other treatments (p≤0.05) while the control possessed the highest sucrose content. The H-10 and H-15 treatments resulted in lower water activity and water mobility than other treatments. This reflected that the monosaccharides present in these samples bind more water in the final product. For texture, the H-15 had the lowest hardness and cutting work but this was not significantly different from those of H-10 (p>0.05). The highest hardness and cutting work was found in P-15. The color of products obtained from all treatments were in the shade of red while the control gave the highest L* and a* values (p≤0.05). From sensory evaluation, it was shown that the H-15 was the most acceptable. The bacteria, yeast and mold counts of all treatment stayed within the levels set for dried fruit products by the Thai Industrial Standards Institute (TIS 919-1989). The microstructure analysis of osmosed and dried products showed that the cell structure of H-10 and H-15 was less shrinkage than other treatments.