Abstract:

Four different extraction processes, namely sulfuric acid treatment, sodium hydroxide treatment, sequential treatment with sulfuric acid followed by sodium hydroxide and sequential treatment with trypsin followed by sulfuric acid were used to obtain total dietary fiber (TDF) from tomato skin, a byproduct of the tomato paste industry. The physicochemical properties (waterholding capacity, oil-holding capacity, swelling capacity, cation-exchange capacity and bile salt adsorption capacity) of the obtained TDF products were determined. Among the four extraction processes, sequential treatment with trypsin followed by sulfuric acid gave the best removal of impurities and the resultant product presented the highest soluble dietary fiber content and the best color. The proximate chemical composition and physico-chemical properties of the TDF products obtained using the four extraction processes were obviously different from those of the raw material. Both the TDF products obtained by sodium hydroxide treatment alone and in combination with sulfuric acid treatment had higher water-holding capacity (7.85 g/g and 8.7 4 g/g, respectively) and swelling capacity (4.9 mL/g and 5.5 mL/g, respectively), and the oil-holding and bile salt adsorption capacities of those obtained by sulfuric acid treatment alone and in combination with trypsin treatment were both high, reaching up to 5.49 g/g and 5.91 g/g, and 297.3 mg/g and 329.4 mg/g, respectively. Except sequential treatment with trypsin followed by sulfuric acid, all the three other extraction processes yielded TDF products with a cation exchange capacity higher than that of the raw material.

Key words: tomato skin, dietary fiber, preparation method, physico-chemical properties