Frozen Carrots Texture and Pectic Compotients as Affected by Low‐Temperature‐Blanching and Quick Freezing

Abstract

MATERIALS & METHODESCarrots preheated for 2 hr at 60°C and then cooked became firmer than raw or cooked carrots. After preheating, the amount of high methoxyl pectin decreased, and low methoxyl pectin increased. Firmness of carrots decreased through freezing then thawing, but preheated carrots retained firmer texture than those blanched in boiling water. Quick-freezing resulted in better texture than slow-freezing. Loss in texture was accompanied by release of pectin. Slow-freezing accelerated release of pectin as compared to quick-freezing. Preheated carrots were slower in release of pectin. The degree of esterification of pectin substances in raw carrots decreased during preheating, freezing and thawing. Cell damage in quick frozen carrots was slight. Optimum preheating occurred with 30 min at 60°C or 5 min at 70°C. Preheating and then quick freezing were effective in improving texture of frozen carrots. Sample preparationThe cortex parenchyma of carrot roots (Daucus carota L. cv. Kuroda Gosun ninjin) grown in Okayama, Japan, were cut into 2g disks (11 mm thick and 15 mm diameter). The disks were divided into I7 lots for procedure -A and 60 lots for procedure -B, respectively. Three disks were used for each lot. Experiment was repeated two times.Blanching, freezing and thawing A-Effects of low-temperature-blanching and quick freezing on texture and pectic change. Disks were preheated for 2 hr at 60°C (lowtemperature-blanching) or blanched for 3 min in boiling water (hightemperature-blanching). Raw, blanched or preheated disks were sealed into polyethylene bags and then frozen at -35°C for 2 days using a conventional freezer (Sanyo Medical Freezer, Sanyo Denki Co., Tokyo), or were also frozen with liquid nitrogen (freezing rate: -5"C/min, f&al temo. -50°C) using a nrogram freezer (Cooline Master CM-Mark II. Tai;o Sanso 'Co., ?okio).-Disks were &awed For 30 min at 20°C 0; were also thawed for 3 min (raw and blanched disks) or for 6 min (preheated disks) in boiling water. For comparison, raw and preheated disks were cooled for 6 min in boiling water.

Osmodehydrofreezing of sensitive fruit and vegetables: Effect on quality characteristics and shelf life

“…Calcium chloride was also contributed to increased firmness due to the interaction of calcium with pectins and other cellular wall components of the plant cellular matrix (Gras et al, 2003). Fuchigami, Miyazaki and Hyakumoto (1995) observed that the worsened texture of frozen tomatoes was accompanied by a decrease in the content of pectic compounds. Lisiewska and Kmiecik (2000) also reported that the level of protopectins and pectins were significantly reduced by the freezing process itself and during subsequent frozen storage of tomato tissue.…”

The thermomechanical properties of carrot cell wall material

“…Contract/grant sponsor : Biotechnology and Biological Sciences Research Council. heating process. This work was also complemented by Fuchigami et al (1994Fuchigami et al ( , 1995 who studied the e †ect of freezing and thawing by characterising the Ðrmness with a creepmeter. Other methodology was adopted by Ramana and Taylor (1992a,b) who evaluated the rheological properties respectively on carrot discs and carrot cell and cell wall suspensions by oscillatory measurements during freezing and cooking.…”

Effect of Standing After Preheating on the Softening Rate of Root Vegetables

“…In particular, preheating of various vegetables such as potato (Bartolome and Johan, 1972;Abu-Ghannam and Crowley, 2006), sweet potato (Truong et al, 1998;Fuchigami et al, 2002), and carrot (Fuchigami et al, 1995;Ng and Waldron, 1997;Smout et al, 2005) has been investigated. However, most examinations of vegetable preheating have been carried out for 30 min to 2 h in hot water, which might cause the elution of water-soluble components.…”