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Starch/Stärke 2014, 66, 1013–1021 1013 DOI 10.1002/star.201400104 RESEARCH ARTICLE Impact of acid and heat–moisture treatment combination on physicochemical characteristics and resistant starch contents of sweet potato and yam starches Pham Van Hung 1, Nguyen Thi Huyen My and Nguyen Thi Lan Phi 2 School of Biotechnology, International University, Vietnam National University in HoChiMinh City, HoChiMinh City, Vietnam Faculty of Chemical Engineering, HoChiMinh City University of Technology, HoChiMinh City, Vietnam The objective of this study is to investigate formation of slowly digestible starch (SDS) and resistant starch (RS) and change in physicochemical properties of sweet potato and yam starches under a combination of acid and heat–moisture treatments using three mild organic acids including acetic acid, lactic acid and citric acid and heating temperature at 110°C for h The results show that the SDS and RS in sweet potato starch significantly increased from 6.6 and 14.7% in native starch to 8.7–13.2% and 37.5–42.1% in acid and heat–moisture treated starches, respectively Likewise, the SDS and RS in yam starch increased from 4.7 and 21.6% in native starch to 10.0–11.3% and 39.0–46.4% in the treated starches, respectively The RS content in the acid and heat–moisture treated starches was also significantly higher than that of the heat–moisture treated starches without acid hydrolysis Yam starch produced higher amount of RS under acid and heat–moisture treatment as compared to sweet potato starch at the same condition Swelling power and viscosity of starches significantly decreased, whereas the solubility significantly increased after treatments The citric acid had the most impact on RS formation and starch properties, followed by lactic acid and acetic acid As a result, the combination of acid and heat–moisture treatment is a useful method to produce higher amount of resistant starch, which can be applied for functional foods Received: May 29, 2014 Revised: July 8, 2014 Accepted: July 14, 2014 Keywords: Acid hydrolysis / Heat–moisture treatment / Resistant starch / Sweet potato / Yam Introduction Starch, the most abundant reserve carbohydrate of many plants, is also a major component of many food products Starch in foods after consumption can be classified into three types based on their digestibility: a rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant Correspondence: Dr Pham Van Hung, School of Biotechnology, International University, Vietnam National University, Quarter 6, Linh Trung Ward, Thu Duc District, HoChiMinh City, Vietnam E-mail: pvhung@hcmiu.edu.vn Fax: ỵ84-8-37244271 Abbreviations: HMT, heatmoisture treatment; RDS, rapidly digestible starch; RS, resistant starch; SDS, slowly digestible starch; SPS, sweet potato starch; YS, yam starch ß 2014 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim starch (RS) [1] RDS and SDS are completely digested and absorbed in the human small intestine that cause the increase in blood glucose level, whereas RS escapes digestion in small intestine and does not contribute to the blood glucose level of healthy individuals Recently, the SDS and RS have received much attention for both its potential health benefits and functional properties The SDS are known to have potential health benefits in a stable glucose metabolism, diabetes management, mental performance, and satiety [2] The SDS may be used by athletes to provide a longer-lasting source of systemic glucose [3, 4] Although RS is not digested, it is fermented in the large intestine by human microflora to produce short-chain fatty acids The potential health benefits of RS have been reported as prevention of colon cancer, hypoglycemic effects, substrate for growth of the probiotic microorganisms, www.starch-journal.com 1014 V H Pham et al reduction of gall stone formation, hypocholesterolemic effects, inhibition of fat accumulation, and increased absorption of minerals [5] Therefore, the recent studies focus on production of high amounts of RS from various starch sources and application of RS as a “low-carbohydrate” ingredient in food formulations [3] SDS and RS can be produced by various modification techniques including physical, chemical, and enzymatic modifications Heat–moisture treatment (MHT) is a wellknown hydrothermal method to increase the levels of SDS and RS in starches without destroying their granular structure [6] In HMT, starch granules are treated at low moisture levels (
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