Improvement of resistant starch content and baking quality of cross-linked soft rice flour.

To increase resistant starch (RS) content of rice flour, soft and normal rice flours were cross-linked with different flour concentrations (40, 50%). RS contents, morphology, and baking qualities of cross-linked Singil rice flour (CSRF) and Hopyeong rice flour (CHRF) were compared. Amylose and protein contents of Singil flour were higher than those of Hopyeong flour. The protein content of CSRF maintained but that of CHRF reduced. Although the RS content increased after cross-linking, the degree of RS was higher 50% flour than 40% flour. The shape of cross-linked rice flour particles changed into starch granules with debris. The overall quality and texture of CSRF40 cupcake showed the highest scores by preference test. These results suggest that CSRF can be used as a high RS rice flour substitute for wheat flour, because soft rice is easy to make flour.

Methods to improve rice protein dispersal at moderate pH.

Dispersion of rice protein (RP) at a neutral pH is highly important for its application in the food industry. We analyzed the solubility of RP at different pH conditions and found higher solubility at pH < 3 and pH > 8 than at a neutral pH. Furthermore, at pH 2, the RP solubility improved from 30 to 63% with sonication; however, the samples precipitated when the pH was increased from 2 to 7. To circumvent this, anionic pectin and sodium alginate were added to the RP solution at pH 2. Pectin formed a complex with RP at pH 2, showing a shift in the zeta-potential from 17.3 mV (RP only) to - 1.0 mV (RP plus 1% pectin). Interestingly, the formation of this RP-pectin complex allowed RP to remain dispersed when the pH was increased to 7. Moreover, a stable emulsion could be prepared using the RP-pectin complex as an emulsifier.

Preparation of functional rice cake by using ß-carotene-loaded emulsion powder.

The purpose of this study was to apply a powdered ß-carotene-loaded emulsion to a real food product, Korean traditional rice cakes (Garaedduk). ß-Carotene was incorporated into the oil phase of a sodium caseinate-stabilized emulsion. Emulsion powder containing ß-carotene was prepared using freeze-drying, and maltodextrin and gum arabic were used as wall materials. Oil/protein/maltodextrin weight ratios of 3:1:2 and 3:1:5 (core-to-wall ratios of 1:1 and 1:2) were used, and gum arabic was added by replacing the amount of maltodextrin for 0.1%, 0.2%, and 0.5% w/w. Manufactured emulsion powders prepared with wall material at a core-to-wall ratio of 1:2 remained stable after reconstitution in terms of particle diameter and ζ-potential. The encapsulation efficiency of the emulsion powder increased by 90% in the presence of maltodextrin at a core-to-wall ratio of 1:2. Garaedduk containing the emulsion powder was then manufactured and it was confirmed that ß-carotene was not degraded during the manufacturing process of Garaedduk by using HPLC. The results from this study may be useful for rational designing of functional foods with lipophilic bioactive materials.

Preparation and characteristics of octenyl succinic anhydride-modified partial waxy rice starches and encapsulated paprika pigment powder.

Physicochemical properties and emulsion stability of octenyl succinic anhydride (OSA)-modified partial waxy rice Baegjinju starches which were made with different OSA additions and the color stability of the encapsulated paprika pigment powder using the OSA starch were investigated. The DSs of the OSA starches ranged from 0.0152 to 0.0269. The band at 3303 cm-1 reduced as the OSA levels increased, but the A-type crystallinity was maintained. The oil absorption and emulsion stability, the short chain (DP6-12) amylopectin, the resistant starch levels, and the peak and final viscosities increased as the OSA levels increased. The encapsulated pigment powder with freeze-drying had higher color stability and better emulsion, and heating stabilities occurred with spray drying and the native pigment. From these results, it is suggested that the OSA-modified Baegjinju rice starch is a good wall material to protect lipophilic carotenoids. The encapsulated pigment powders could be used as stable natural colorants.

Properties and Digestibility of Octenyl Succinic Anhydride-Modified Japonica-Type Waxy and Non-Waxy Rice Starches.

Waxy and non-waxy rice starches from japonica type Korean rice varieties were esterified with different levels of octenyl succinic anhydride (OSA), and the molecular structure of amylopectin (AP), digestibility, and emulsion stability were investigated. As OSA levels increased, the degree of substitution, granule size, peak and final viscosities, emulsion stability, and short chain of AP increased. However, the gelatinization temperature and enthalpy, and digestibility decreased. All OSA esterified starches showed a new band at 1723 cm-1, but maintained A-type crystallinity. The DP6-12 of AP in waxy rice starch (WRS) was higher than that in non-waxy rice starch (NRS) with increasing OSA levels. Because the amylose and long chain of AP accessed easily with OSA groups, the digestibility of NRS was lower than that of WRS. The emulsion stability was higher in WRS than in NRS. From the above results, it is suggested that amylose should have a higher affinity with OSA esterification than AP and that the emulsion stability should increase in WRS, but the digestibility should decrease in NRS after OSA modification.

Textural character of sweet potato root of Korean cultivars in relation to chemical constituents and their properties.

A relationship between chemical constituents and physicochemical and textural properties of different Korean sweet potato (SP) cultivars were investigated in terms of the hardness of raw and cooked root, alcohol insoluble solid (AIS), starch and amylose content, amylase activities, and pasting properties. Correlation coefficients were analyzed and principal component analysis was performed. The hardness of cooked root was found to correlate with the hardness ratio of cooked/raw SP, AIS content (0.75**), starch content (0.64**), and peak viscosity of SP powder (0.56*). It was discovered that SP cultivars could be classified into mealy (Sincheonmi, Daeyumi, Sinyulmi), intermediate (Dahomi, Sinjami, Geonhwangmi, Yeonjami, Pungwonmi), and waxy (Juhwangmi, Sinhwangmi) types depending on the first principal component (PC1, 68%). Therefore, it was found that the texture types of SP cultivars could be predicted from hardness of cooked root and are in relation to AIS and starch contents, and peak viscosity of raw powder.

Effects of newly developed waxy rice flour on the quality characteristics and oxidative stability of Korean traditional fried cookie, Yakgwa.

The effects of waxy rice flour (WRF) in substitution for wheat flour (WF) on the oil absorption, structure, texture and oxidative stability of traditional Korean fried cookies, Yakgwa, were investigated. Fried cookie prepared with WF showed the greatest oil absorption (20.66%), however, the oil absorption reduced as the ratio of WRF substitution increased. The fried cookies prepared with WRF in substitution for WR showed the reduced oil absorption and increased oxidation stability. In addition, the cookies still maintained a layered structure with crispiness and softness. Also, when white WRF was used, the fried cookie showed the increased oxidative stability and reduced oil absorption decreased compared to when brown WRF was used. WRF can be used as a substitute for WF at a percentage of up to 75% and can improve the structure and oxidative stability of Yakgwa during storage. Substitution of WRF for WF significantly improves the structure and oxidative stability of Yakgwa.

Molecular structures of rice starch to investigate the differences in the processing quality of rice flours.

The molecular structures of non-waxy rice starches purified from three Korean rice cultivars, Dongjin1, Hopyeong, and Ilmi, were investigated to determine the main reasons why it is difficult to make manju with Dongjin1 flour compared to other rice flours with similar processing qualities. The molecular structural characteristics of the three rice starches were analyzed by high-performance size-exclusion chromatography and high-performance anion-exchange chromatography. The Dongjin1 starch had lower molecular weight (MW) amylose, a smaller proportion of short a chains, and higher average amylopectin branch chain length than the other two starches. These properties of Dongjin1 starch resulted in a lower water binding capacity, lower swelling power at 80 °C, and lower peak viscosity than those of the other two starches. It is suggested that the MW of amylose and degree of polymerization of amylopectin are important factors to make gluten-free bakery products using non-waxy rice flours.

Preparation and stability of resistant starch nanoparticles, using acid hydrolysis and cross-linking of waxy rice starch.

To develop resistant starch (RS) nanoparticles, waxy rice starch was hydrolyzed with acid for 10 days, and acid-hydrolyzed waxy rice starch (AHW) was cross-linked with sodium trimetaphosphate. The RS nanoparticles were collected by freeze-drying (FD), freeze-drying after sonication (SFD), and ethanol dehydration after sonication (SE). The particle size distribution, RS level by modified AOAC, zeta potential, and stability of dispersion were assessed. The hydrolysis rate ranged from 44.62% to 49.43%, and AHW particle size decreased as hydrolysis time increased. All AHW and RS nanoparticles showed A type crystallinity. The particle size and zeta potential of the nanoparticles dried by FD, SFD, and SE were 300.0, 211.9, and 459.7 nm and -37.1, -43.0, and -35.4 mV, respectively. The RS levels were increased by cross-linking. The SFD dispersion was the most stable. The results indicate that the RS4 nanoparticles, for applying to liquid foods, can be prepared by acid hydrolysis, cross-linking, and SFD.

Anti-oxidant activities of mung bean starch and starch gels prepared from whole and hulled seeds.

Anti-oxidant activities of ethanol extracts from whole and hulled mung bean starches (WMS and HMS) isolated using distilled water, and gels (WMSG and HMSG) were investigated. Total chlorophyll contents of WMS and WMSG were 4.61 and 2.14 µg/mL, respectively. WMS at 0.29 mg of gallic acid/g of MS and 0.54 mg of quercetin/g of MS had higher total phenolic compounds and flavonoid contents than HMS at 0.11 mg of gallic acid/g of MS and 0.28 mg of quercetin/g of MS. Total phenolic contents of WMSG and HMSG increased by 2.14x and 1.64x, respectively. Total flavonoid contents decreased by 0.98x and 0.57x. The 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) diammonium salt radical scavenging activities and reducing powers of WMS and WMSG were higher than for HMS and HMSG. Cheongpomuk made using WMS exhibits increased anti-oxidant activities of gels and is a good food for improvement in health functionality.

Textural properties of mung bean starch gels prepared from whole seeds.

The textural properties of mung bean starch gels (MSG) made by starches purified from whole seeds of Dahyeon were investigated to improve the quality of Korean traditional starch gel, cheongpomuk. Based on our investigation, the protein and dietary fiber contents of starch from whole mung beans (WM) were significantly higher than those from hulled mung beans (HM); however, apparently, WM had lower amylose contents than HM (their respective apparent amylose contents were 32.42 and 33.09%). The fresh gels (WMSG and HMSG), stored gels (WMSG-S4 and HMSG-S4), and reheated gels (WMSG-R4 and HMSG-R4) were also compared. The stored gels showed the highest L and b values, translucence, hardness, and gumminess. While HMSG showed a denser network structure than WMSG, the structure of stored gels was recovered after reheating. The fresh gels showed V type crystallinity, but the stored gel changed into B type crystallinity. WMSG showed higher sensory bending properties and smoothness than HMSG, but more similarities in the overall qualities.