Effect of drying on antioxidant property and starch digestibility of sweet potato

Name: Desale, Fessehaye Hdremariam

Organization : Mae Fah Luang University

keyword: Sweet potato

LCSH: Drying

Classification :.LCCS: TX553.A73

LCSH: Sweet potatoes -- Health aspects

LCSH: Antioxidants

Abstract: The presence of high moisture in fresh roots of sweet potato (Ipomea batatas) limits its storage and usage for longer period of time. Reduction of product moisture content by drying is a most common postharvest technique for prolonging shelf life of agricultural materials. However, drying also affects the quality of products in many ways.This research has been conducted on two sweet potato cultivars, orange fleshed (OFSP) and purple fleshed (PFSP) at three drying temperatures 55, 70 and 85℃ taking freeze drying as a reference treatment. The aims were 1) to compare the nutritional quality between orange fleshed and purple fleshed sweet potato varieties, 2) to study the effect of drying at different drying temperatures on antioxidant property of sweet potato flour and 3) to study the effect of drying at different drying temperatures on starch digestibility and functional properties of sweet potato flour. The fresh roots from the two varieties were analyzed for their proximate compositions of moisture, protein, fat, lipid, ash, carbohydrate and fiber content. For drying experiment, OFSP and PFSP roots were washed with tap water, peeled and sliced to uniform pieces. Slices were subjected to hot air drying at different drying temperatures of 55, 70 and 85℃ and drying time of 4.0, 3.0 and 2.0 hours, respectively to a moisture content below 8% (wb). To be used as a comparison, slices were mashed and freeze dried. All dried samples were powdered and analyzed for their physicochemical and starch related functional properties; moisture content (mc), water activity (aw), color, pasting and gelatinization properties. The bioactive compounds in terms of total phenolic contents (TPC), total carotenoid content (TCC), total anthocyanin content (TAC), antioxidant properties based on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assay were analyzed. In addition, starch digestive properties in terms of resistant starch (RS), non-resistant starch (NRS) and percentage starch digestion were evaluated. Results of proximate composition showed that, OFSP had higher contents of protein and fat, but lower in dry matter, ash and carbohydrate contents than PFSP. Drying reduced the mc of fresh roots to safe levels of 3.11 to 7.49%wb with a corresponding aw levels of 0.15 to 0.52. The lightness and yellowness of hot air dried samples were higher than freeze dried samples and the increase was more apparent with the increase in drying temperature. Drying did not cause any apparent effect on starch granule structure in both the varieties. Analysis on functional properties, showed that an increase in peak viscosity (PV) of dried samples which also increased with increasing of drying temperature in both the varieties. Other pasting viscosities; trough viscosity (TV), final viscosity (FV) and setback viscosity (SBV) in freeze dried sample were higher than hot air dried samples in OFSP indicating to more tolerance to heat and shearing of freeze dried sample than hot air dried samples. In PFSP, all the pasting viscosities were higher in the hot air dried sample with progressive increase as drying temperature increases. Similarly to pasting properties, gel hardness was higher in freeze dried sample in OFSP than hot air dried samples while it was the vice versa in PFSP. No significant effect due to drying was noticed in gelatinization temperature and enthalpy of gelatinization of samples. Drying significantly affects the bioactive compounds and antioxidant properties of sweet potato. Reduction in TPC, TCC and FRAP assay in hot air dried samples than the freeze dried samples in OFSP was seen in this study and the decrease was more evident at higher drying temperatures. In PFSP, hot air drying resulted to a better antioxidant activities of both FRAP assay and DPPH scavenging activity; whereas at higher drying temperatures the TAC significantly decreased. Exceptionally, the 55℃ dried PFSP sample showed much higher value in all the bioactive compounds and antioxidant properties than other samples. Changes in antioxidant properties due to drying were significantly positively correlated to the changes in bioactive compounds due to drying in both the varieties. A slight increase in amylose content and resistant starch contents in hot air dried samples than the freeze dried samples was observed in both the varieties. The change in NRS was also observed accordingly. Based on in-vitro digestibility, percentage starch digestibility increased after hot air drying. However, there was no significant correlation between RS, NRS and percentage starch digestibility of dried sweet potato.

Mae Fah Luang University. The Learning Resources and Education Media Center

Address: Chiang Rai

Email: library@mfu.ac.th

Name: Rungarun Sasanatayart

Role: Advisor

Created: 2016

Issued: 2560

Modified: 2020-04-29

Issued: 2017-09-13

วิทยานิพนธ์/Thesis

application/pdf

CallNumber: Thesis TX553.A73 D441e 2016

eng

DegreeName: Master of Science

Level: Master's Degree

Descipline: Technology Management of Agricultural Produces

Grantor: Mae Fah Luang University

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