Structural modification by different pretreatment methods to enhance microwave-assisted extraction of β-carotene from carrots

Since the structure of a material is a key factor influencing the extraction efficiency, any means to modify the structure to enhance extraction is attractive. As limited information is available on the effect of sample pretreatment prior to extraction on the extractability of a bioactive compound, the effects of selected pretreatment methods, i.e., soaking in citric acid, blanching in water as well as in citric acid, on the sample structure and subsequent microwave-assisted extraction (MAE) were investigated; carrots and beta-carotene (as well as carotenoids) were selected as the test material and bioactive compound, respectively. A suitable condition to extract beta-carotene in terms of the microwave power and extraction time was determined. Comparison between MAE and Soxhlet extraction was also made. At the optimized condition the contents of beta-carotene and total carotenoids extractable from carrots blanched in water (29.74 and 58.04 mg/100 g dry basis) and in citric acid (32.08 and 61..62 mg/100 g dry basis) were significantly higher than those from the untreated carrots (23.26 and 51.79 mg/100 g dry basis). The antioxidant activities of the extracts obtained from carrots blanched in water and in citric acid were also higher than that from carrots with no pretreatment. Comparison between MAE and Soxhlet extraction revealed that the extract from MAE contained lower amounts of beta-carotene and total carotenoids and exhibited lower antioxidant activity; the required MAE time was significantly shorter, however. (C) 2012 Elsevier Ltd. All rights reserved.