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.

Raw and blanched carrots (3 min, boiling water) were frozen at -2"C, -3"C, -4°C or -5"C/min (final -20°C or -50°C) then thawed at 20°C or 100°C. Firmness of thawed raw carrots was: -5°C > -4°C > -3°C > -2"Umin. Effect of freezing rate on blanched carrots was less than that on raw carrots, but firmness of thawed carrots was not affected by final temperature of freezing. When raw carrots were thawed at 2O"C, high methoxyl pectin decreased. Pectin decrease in blanched carrots caused by freezing was greater than that in frozen raw carrots. Effects of slow-freezing, programmed-freezing (slow + quick + slow) and quick-freezing showed quick freezing (-S"C/min) best for texture. As freezing rate decreased, drip increased. A wide difference among experimental samples in fine structure was revealed by cryo-scanning electron microscopy.

The pectins of Japanese radish roots were fractionated by successive extraction with three reagents: diluted HCI, sodium acetate buffer, and sodium hexametaphosphate solutions. The tissue, softened by thermal maceration, contained more HCl-soluble pectin (PA) than the sodium acetate buffer soluble pectin (pB). The degree of esterification (DE) of pA was higher than that of pB. With CaCI,, pB formed some precipitates, but pA did not. The elution patterns of pA and pB by DEAE-cellulose column chromatography were different. A clear relationship between other dietary fiber (hemicellulose, cellulose and lignin) and softening of roots was not observed. The composition of pectins, especially DE, appeared to have an effect upon the texture of the Japanese radish softened during cooking.

Raw or 3 min blanched carrots were pressurized for 45 min at Ϫ18ЊC ϳ Ϫ20ЊC and then thawed at 20ЊC. When carrots were frozen at 100MPa (ice I), firmness decreased and strain increased. Textural values of carrots pressurized at 200MPa (liquid), 340MPa (ice III), 400MPa (ice V) at ca. Ϫ20ЊC were acceptable. When pressure was increased above 500MPa, the strain increased. Release of pectin and histological damage in carrots pressurized at 200, 340 and 400MPa were less than carrots frozen at 100 and 700MPa (ice VI). After pressurization at 200 and 340MPa at Ϫ20ЊC, carrots were stored in a freezer (Ϫ30ЊC). Firmness decreased and strain increased, but textural values were higher and histological structure were more intact than those frozen at Ϫ30ЊC (0.1MPa) then stored. Thus, high-pressure-freezing at 200, 340 and 400MPa appeared to be effective in improving both the texture and histological structure of frozen carrots.