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

Abstract

Results are presented of the effect of freezing followed by thawing (air and water immersion, both at environmental temperature) and cooking (traditional boiling in a covered pot) on quality profile (in terms of objective texture, colour, chlorophylls and pheophytins and sensory attributes) and structure of green beans (cv. Win). Freezing was carried out at three different rates by forced convection with liquid nitrogen vapour. Kramer shear cell (KSC) and Warner-Bratzler (WB) tests were used for objective assessment of the texture. The highest parameter values occurred in beans frozen at the highest rate and air-thawed at the slowest rate. Also, minimum alteration of the rheological behaviour of cooked beans was achieved by freezing at the highest rate. The best parameter for assessing the texture of frozen green beans after thawing and cooking was the Warner-Bratzler slope (S WB ). Coefficients of softening estimated for S WB in the thawed beans showed that the texture of the beans frozen at -24 °C was almost 4 and almost 5 times softer than that of the beans frozen at -70 °C, for air and water thawing respectively. Frozen and thawed green beans were darker than fresh control, whereas freezing prior to cooking produced lighter-coloured beans than direct cooking. The freezing rate affected colour parameters differently depending on the process that followed. When beans were thawed, increasing the freezing rate produced lighter-coloured beans, whereas when beans were cooked, increasing the rate produced darker-coloured beans. No difference was found in sensory assessments between cooked samples frozen at -24, -35 and -70 °C, which probably reflects the panellists' mixed preferences for quickly and slowly frozen samples. Scanning electron microscopy (SEM) revealed different degrees of mechanical damage to tissue structure, which accounted for the rheological behaviour of the beans.

Towards a better understanding of the pectin structure–function relationship in broccoli during processing: Part I—macroscopic and molecular analyses

“…This decline is assumed to be attributed to an increase in PME activity during pretreatment, resulting in an extended de-esterification of pectic HG. This phenomenon has previously been demonstrated by different authors (Canet, Alvarez, Luna, Fernandez, & Tortosa, 2005;Ni et al, 2005;Sila et al, 2004;Wu & Chang, 1990). As can be seen in Table 1, enzymatic de-esterification occurred to a larger extent in HPpretreated samples than in LTB-pretreated ones.…”

Influences of Pretreatments and Drying Process Including Fluidized Bed Puffing on Quality Attributes and Microstructural Changes of Banana Slices

“…A longer blanching time and lower puffing temperature were responsible for the higher shrinkage. The high shrinkage for the blanched sample can be explained considering that some cell components are solubilized and degraded during blanching [25] and the starch is gelatinized. These effects cause higher shrinkage of blanched banana during the first stage of drying and the formation of dense layer with a rigid structure.…”

Effect of Processing on Antioxidants and Their Activity in Dietary Fiber Powder from Cabbage Outer Leaves

“…This is possibly due to the fact that slicing caused damage to plant tissues and hence facilitated solubilization and degradation of water-soluble components including pectin from the plant cells during blanching. [26,27] Loss of pectin led to softening of plant tissues and hence higher rates of water removal in the cases of SWB and SSB samples. [28] The evolutions of selected antioxidants during drying are shown in Fig.…”