The effect of ohmic heating pretreatment on the quality of frozen vegetable production

Nowadays, alternative methods to commercially used food processing methods are being investigated. One of these methods used to produce foods with high nutritional value and quality is the ohmic heating technique which takes its name from the ohm's law. In this study, ohmic heating pre-treatment was used as an alternative to the conventional blanching process in order to improve the product quality in the frozen food process. Freezing is one of the methods that provide the best preservation for the taste, structure, appearance, color, flavor and composition of the vegetables. For this purpose, frozen green beans (Phaseolus vulgaris L.), which are widely preserved by freeze production, were used. Firstly the stems were removed and the vegetable was cut to a length of 40-60 mm. One part was blanched in the ohmic heating apparatus and the other part was blanched by the conventional method until the peroxidase enzyme was inactive. Then both vegetables were frozen by using IQF. Some of the conventional blanced beans representing home production were also allowed to freeze slowly in the freezer. The products were stored for 12 months in the frozen warehouse. During the storage, they were evaluted for total phenolic content, antioxidant capacity, chlorophyll a, chlorophyll b, total chlorophyll amount and color. Also contents and presence of total live microorganisms, yeast-mold, total coliform, Escherichia coli, Listeria monocytogenes and Escherichia coli O157: H7 were analyzed. As a result, the antioxidant capacity of the ohmic heating method (7,41 mmol TE/100 g DM), was decreased more than the traditional method and house type. While the total amount of phenolic matter (0,29 mg/g DM) was increased compared to the home type traditional method, it was reduced compared to conventional method. The amount of chlorophyll (8,85 mg/100g DM) and color values were better preserved in frozen beans blanched with ohmic heating. Statistically, different blanching methods caused significant difference between all the parameters examined except chlorophyll amounts. While the differences between the chemical analysis results were significant during storage, blanching method and storage time interaction did not differ only in terms of color values (except L and c values) (p <0,05). According to the results of microbiological analysis, the number of microorganisms in fresh beans decreased in all processing conditions and the products were found to be reliable especially in terms of pathogens.