[6-1130-P] Postharvest/Food Technology and Process Engineering (6th)

[6-1130-P-20] Effects of Blanching Pretreatment on Drying Characteristics and Pectic States of Dried ‘Fuyu’ Persimmon

*Tatsuya Oshima¹, Kodai Kato¹, Satoshi Iwamoto¹, Teppei Imaizumi¹ (1. Gifu University(Japan))

Keywords:pectin, atomic force microscope, drying, blanching, persimmon

‘Fuyu’ persimmon is popular in Japan and distributed not only as fresh fruits but also dried ones. Although fruits and vegetables are often dried by hot air, length of the drying time is considered as a big problem. To improve drying efficiency, blanching treatment is sometimes applied prior to drying. However, for ‘Fuyu’ persimmon, effects of these processes on drying characteristics and quality-related components are not clarified sufficiently. Among components in fruits, pectic substances are known to contribute to texture formation. Additionally, functional aspects of the substances, such as intestinal regulating function and prebiotic effect, also attract attention. Thus, we investigated drying characteristics and changes in pectin states during several drying treatments including blanching. Persimmon fruits (cv ‘Fuyu’) harvested in Gifu city was used in this study. The persimmon flesh was cut into cylinder (20.5 mm diameter and 10 mm height) using a cork borer and a knife. The initial moisture content of the sample was 5.06 (dry basis). In this study, we prepared blanched and non-blanched samples. For the blanched one, the persimmon samples were immersed in hot water at 95 degree for 2 min, then immediately cooled in iced water for 2 min. Both of the blanched and the non-blanched samples were dried in a forced hot air oven controlled at 40, 50, 60 and 70 degree. During the drying, sample weight was weighed at every hour, and converted to moisture content. A model was fitted to measured value and rate constant k (h^-1) of the drying process was calculated for each temperature. Next, alcohol insoluble solid (AIS) of the samples, which dried at 40 and 60 degree until 2.0 and 0.3 (d.b.), was prepared to extract pectin. Pectin fractions were sequentially extracted from AIS with distilled water, 0.05 M CDTA solution and 0.05 M Na₂CO₃ + 20 mM NaBH₄ solution, and water-soluble pectin (WSP) fraction, chelator-soluble pectin (CSP) fraction and diluted alkali-soluble pectin (DASP) fraction were collected, respectively. Galacturonic acid content in pectin fractions were determined using carbazole sulfuric acid method. Also, atomic force microscopy (AFM) observation was performed. Extracted pectin fractions were diluted 200 times with distilled water. A 3 μl of the resulting solution was dropped onto freshly cleaved mica, then it were dried overnight at room temperature. An AFM5400L (Hitachi High Technologies) was used for imaging in the dynamic force mode. A silicon cantilever with nominal spring constant of 15 N m^-1 and resonant frequency of 110-150 kHz was used. The scanning area was set at 2 µm × 2 µm in the XY plane, and the scanning resolution was 512 × 512 points. AFM images were morphologically analyzed using the SPIP software. Regardless of whether it was blanched sample or not in the drying process, the exponential model could be fitted (R²=0.9962 - 0.9996). Comparing the obtained rate constants, blanched samples had high value, which indicating blanching is effective to improve the drying process. In addition, we prepared dried samples having 2.0 and 0.3 of moisture content (d.b.) and evaluated state of pectin in these samples. After the blanching, the ratio of WSP amount in total pectin obviously decreased, and the ratio of CSP and DASP increased. However, the ratio of WSP increased with drying in all samples. At 0.3 of moisture content (d.b.), Overall, the blanching treatment indicated greater effect on pectin composition than the drying process. In AFM images of pectin nanostructure, short chain and granule like objects were appeared in WSP. Also, lager structures were observed in CSP. The result in this study shown that drying treatment and blanching pretreatment changed pectin composition and structure. Thus, we assumed that texture and functional properties of dried products will be modified by selected conditions.