Physicochemical properties of sweet potato starches and their application in noodle products Promotor: Prof. dr. ir. A. G. J. Voragen Hoogleraar in de levensmiddelenchemie Co-promotor: Dr. H. A. Schols Universitair docent departement Agrotechnologie en Voedingswetenschappen Promotiecommissie: Prof. dr. W. Bergthaller (Federal Centre for Cereal, Potato and Lipid Research in Detmold and Münster, Germany) Prof. dr. R. G. F. Visser (Wageningen Universiteit) Prof. dr. E. van der Linden (Wageningen Universiteit) Dr. P. Buwalda (AVEBE, Foxhol, Nederland) Physicochemical properties of sweet potato starches and their application in noodle products Zhenghong Chen Proefschrift ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit, prof. dr. ir. L. Speelman, in het openbaar te verdedigen op woensdag 8 oktober 2003 des namiddags te vier uur in de Aula The research described in this thesis was carried out at the Laboratory of Food Chemistry, Department of Agrotechnology and Food Sciences, Wageningen University, The Netherlands. Zhenghong Chen Physicochemical properties of sweet potato starches and their application in noodle products Ph.D. thesis Wageningen University, The Netherlands-2003 ISBN: 90-5808-887-1 Abstract ABSTRACT Starches isolated from 3 Chinese sweet potato varieties (XuShu18, SuShu2, and SuShu8) differed in granule size and particle size distribution as well as in protein, lipid and phosphorus contents but the amylose contents were similar for these starches (19.3-20.0%). The pasting behavior, swelling pattern, and syneresis properties were investigated and found to vary. On comparison, the physicochemical properties of the sweet potato starches rather differ from those of potato and mung bean starches. The quality of the starch noodle made from SuShu8 starch was well comparable to that made from mung bean starch, and better than that made from SuShu2 and XuShu18 starches as evaluated by both instrumental and sensory analysis. Correlation between starch noodle quality and gel properties of the original starches was established in order to be able to predict the suitability of a starch for starch noodle manufacture. It was found that differently sized granule fractions showed a difference in ash, amylose and phosphorus content, as well as in gel firmness and freeze-thaw stability. The small size (<20 µm) granule fractions were found to be more suitable for starch noodle making and the qualities of both dried and cooked starch noodles made from these fractions were significantly better than those made from their original starches and much better than those made from the large size granule fractions. Sweet potato and potato starches and their derivatives (acetylated and hydroxypropylated) were also evaluated for the ability to manufacture high quality White Salted Noodle (WSN) by replacing the commonly used wheat flour up to 20%. It was found that only the use of acetylated starches could significantly improve WSN quality resulting in decreasing cooking loss, and increasing softness, stretchability and slipperiness. The cold peak breakdown (CPBD) of the composite flour, as measured in 1.5% NaCl solution, showed a significant correlation with the cooking loss, stretch stiffness and stretchability of WSN. Moreover, acetylated starch from potato and sweet potatoes were studied with respect to the degree of substitution (DS) and acetyl group distribution in differently sized granule fractions. The DS of the fractionated starches increased with decreasing starch granule size dimension. The DS of the amylopectin populations of differently sized granule fractions showed the same trends as the original starches, while the DS of the amylose populations were quite constant. It was confirmed that the acetylation only occurred in the outer lamellae of the crystalline region, but took place in all amorphous regions of starch granules. The acetyl group distribution is more heterogeneous in the amylose populations isolated from small size granule fractions. Key words: Sweet potato, starch, noodle, granule, acetyl distribution Contents Contents Abstract Chapter 1 General introduction 1 Chapter 2 Physicochemical properties of starch obtained from three different 19 varieties of Chinese sweet potato Chapter 3 Evaluation of starch noodles made from three typical Chinese sweet 39 Potato starches Chapter 4 Starch granule size strongly determines starch noodle processing and 57 and noodle quality Chapter 5 Improvement of white salted noodle quality by using modified potato 73 and sweet potato starches Chapter 6 Differently sized granules from acetylated potato and sweet potato 93 starches differ in the acetyl substitution pattern of their amylose population Chapter 7 Concluding remarks 111 Summary 131 Samenvatting 135 Acknowledgement 139 Curriculum vitae 143 List of publications 145 General introduction CHAPTER 1 General Introduction 1 Chapter 1 Aim of this research This project was aimed at a better use of abundantly produced sweet potato starches in China. China produces more than 85% of the whole world sweet potato crop. However, this abundant resource is still poorly utilized, in spite of the fact that it is cheaper than other crops. The industrial utilization of sweet potatoes is mainly based on the starch which can be isolated from this crop and which can be used as ingredients for food products. Noodles are important foods consumed in Asian countries. It is estimated that about 30-40 % of total wheat flour consumption is as noodle products in most Asian countries (Miskelly 1993). Starch noodle and Japanese White Salted Noodle (WSN) are the two most popular types, which qualities are mainly affected by starch properties. Starch noodles are made from starch only and the ideal raw material is mung bean starch. High quality WSN is typically made from wheat flour which is imported from Australia. The aim of this research is to evaluate the use of sweet potato starches or their derivatives in the manufacture of high quality of starch noodles in order to replace mung bean starch and in the manufacture of high quality WSN by partially replacing commonly used wheat flour. Starch General introduction Starch is a biopolymer composed of anhydroglucose units and is the major storage energy in various plants in nature. It can be widely found in cereal grain seeds (e.g. corn, wheat, rice, sorghum), tubers (e.g. potato), roots (e.g. cassava, sweet potato, arrowroot), legume seeds (e.g. peas, beans, lentils), fruits (e.g. green bananas, unripe apples, green tomatoes), trunks (e.g. sago palm) and leaves (e.g. tobacco). In Europe, about 7.7 × 106 t of starch is produced annually. It consists of corn starch (49%), wheat starch (29%) and potato starch (22%) (Röper 2002); the global situation is shown in figure 1 and is quite different from the situation in Europe. Starch can be simply manufactured by the combination of grinding the starch-rich crop followed by wet separation techniques. The starch granules will sediment in water due to their higher density. Native starch is a white powder with bland taste and flavor, and insoluble in cold water. In general, cereal starches (e.g. corn, wheat, rice) contain relatively high levels of lipids (0.2-0.8%) and protein (0.2-0.5%) resulting in a lower paste transparency and a pronounced and persistent “raw cereal flavor” of the starch gels. Tuber (e.g. potato) and root (e.g. tapioca) starches have lower levels of lipids (0.1-0.2%) and protein contents (0.1-0.2%). Potato starch is the only native starch containing significant amounts of chemically bound phosphate ester groups (degree of substitution = 0.003 ~ 0.005) located in amylopectin 2 General introduction 9.00% 0.70% 4.20% Corn 7.60% Potato Cassava Wheat Rice and other 78.50% Figure 1-Starch production world wide basis on raw material (International Starch Institute, 1997) Table 1-Chemical characteristics of starches obtained from various sources Starch Amylose (%) Lipids (%) Protein (%) Phosphorus (%) Corn a 28 0.8 0.35 0.00 Waxy corn a <2 0.2 0.25 0.00 High-amylose corn a 50-70 nd 0.5 0.00 Wheat a 28 0.9 0.4 0.00 Potato a 21 0.1 0.1 0.08 Tapioca a 17 0.1 0.1 0.00 Mung bean b 39 0.3 0.3 nd a: from BeMiller and Whistler, 1996; b: from Hoover and others, 1997. nd: not determined. molecules (Table 1). Starch granules are composed of two major polymers: amylose and amylopectin. Their structures and the relative amount of both populations play an important role in determining starch properties. The amylose content and degree of polymerization (DP) of amylose are important for the physical, chemical and technological properties of starch. Most starches contain ca 25% amylose. For waxy starches (e.g. waxy corn, waxy potato) the amylose content 3 Chapter 1 can be less than 2%, while the amylose content of high amylose corn starch can be up to 70% (Table 1). Amylose Amylose is primarily a linear chain of D-glucose units linked by α-1→4 linkages. However, some amylose molecules have about 0.3-0.5% of α-1→6 linkages (branches) (Takeda and others 1990). The DP of amylose is around 1500-6000. DP is the total number of anhydroglucose residues present divided by the number of reducing ends. The total content of carbohydrate generally can be determined by the phenol-sulphuric acid method, while reducing residues can be determined by the Park-Johnson’s colorimetric procedure for glucose (Hizukuri and others 1981). Amylose can form complexes with iodine and various organic compounds such as butanol and fatty acids. The complexing agents are incorporated within the amylose helixes. These complexes are essentially insoluble in water. Amylose is easily leached out from swollen granules just above the gelatinization temperature. The amylose fraction usually can be isolated by such aqueous leaching procedures (Hizukuri 1996), by dispersion and precipitation (Adkins and Greenwood 1969; Ceh and others 1985; Banks and others 1971) and by ultracentrifugation methods (Montgomery and others 1961; Majzoobi and others 2003).