Reprocessing effect on the quality of domestically cooked (boiled/stir-fried) frozen vegetables

Abstract

This was a study of the effect on quality parameters of reprocessing (blanching at 97 °C during increasing times + freezing) prior to domestic cooking (boiling or stir-frying) of frozen green peas (cv. Mastim) and beans (cvs. Paloma and Moncayo). Results were compared with frozen control samples directly boiled or stir-fried. Kramer shear was the most suitable mechanical test for evaluating the effect of reprocessing on mechanical behaviour in both boiled and stir-fried frozen vegetables. Reprocessing significantly affected mechanical behaviour of both green bean varieties with both cooking methods. Reprocessed products were softer than those supplied by the industry, and softening was significantly greater the longer the blanching time. The colour was more uniform and homogenous in boiled than in stir-fried reprocessed vegetables; colour parameters showed that reprocessing affected the colour of stir-fried samples more significantly than that of boiled samples. In all the studied vegetables, less chlorophyll and more ascorbic acid were retained when samples were stirfried than when they were boiled, although chlorophyll and ascorbic acid decreased with increasing reprocessing time in both cooking methods. In the two frozen green bean varieties in particular, SEM microphotographs confirmed the results of mechanical tests, indicating that with both cooking methods, mechanical parameters were lower in the reprocessed samples in the controls. The shortest reprocessing procedure (blanching at 97 °C for 2, 3 min + freezing), as a compromise among quality parameters, could shorten the time required for domestic stir-frying of frozen green peas and boiling or stir-frying of frozen green beans.

Effect of different cooking methods on structure and quality of industrially frozen carrots

“…The decrease of the slope of the rising portion of the curve and the broaden curve profiles of the cooked carrots were probably in relation with the softening and the increased deformability of the structure, due to heat, that caused plasmolysis and cell separations (Fig. 1c-f), as previously observed in other vegetables (Canet et al 2004;Paciulli et al 2015). Among cooking practices, R B and R S samples exhibited very similar forcedistance curves, with narrower shapes than R MW that presented instead a broader curve with a more complex profile ( Fig.…”

“…The test was performed using a 3 mm thick stainless steel knife blade driven through the entire diameter of the vegetable, positioned on a slot surface, at a speed of 3 mm/s. The following parameters were obtained from the force vs distance curves using the application software provided (Texture Expert for Windows, version 1.22): the maximum cutting force values (F max , N), the area under the cutting curve (Area, Nmm), the slope of the linear ascendant portion of the curve (Slope, Nmm ) (Canet et al 2004). Ten slices were analysed for each sample.…”

“…Freezing is one of the most applied methods to process vegetables. Before the consumption, the raw material is subjected to several different steps (blanching, freezing, frozen storage, and final cooking) that greatly impact the final quality of the products (Canet et al 2004).…”

Blanching effects on chemistry, quality and structure of green beans (cv. Moncayo)

“…Frozen ready meals are the largest sector in terms of volume and value, and there is an increasingly wide variety of frozen ready meals available. A whole range of frozen vegetable-based ready meals has been launched by the industry in the last few years in Spain [3]. Marketing is focused on convenience, as these products require only 5-10 min preparation.…”

“…There are several different stages in the production of frozen vegetables during which significant loss of product quality can occur: initial processing (blanching) and preparation prior to freezing; freezing; frozen storage following freezing; and above all, final cooking prior to consumption [3,12]. For example, it is known that the main loss of nutrients in frozen vegetables typically occurs during blanching, a high temperature process which inactivates enzymes that cause deterioration in colour, flavour and odour [6,13,14].…”