紅豆水副產物價值提升之技術

Abstract

紅豆在本草綱目紀載具有利水除溼之功效，其種皮富含植化素，製成紅豆水後具特殊的風味，受到消費者的喜愛，但是在紅豆水生產的過程中，同時會有大量的副產物-水萃後紅豆粒的產生。水萃後紅豆粒其之主要成分(澱粉、蛋白質)皆保留在紅豆粒內部，但因失去原有的色澤和香味，所以利用之機會受限，無法用來製作常見的點心食品，例如紅豆餡，紅豆湯等，目前僅用作飼料使用，非常可惜。本試驗將先探討水萃過程對於紅豆理化性質的影響，並以物理性(乾熱及球磨)、化學性 (酸熱)或酵素性(去分支酵素或蛋白質水解酵素)處理水萃後紅豆粒，分析其組成分變化、豆粉理化性質與其體外消化性質，期望其可提供具機能性(改善全豆粉之澱粉消化性質及糊液黏度)且可多元運用於其他食品系統之素材。水萃後紅豆在豆粉理化性質與生紅豆有明顯差異，紅豆固形物中含有約50%澱粉，但水萃後已有50%被糊化，且其糊液黏度、膨潤力、溶解度和熱焓值均下降，總酚含量則減少約75%，抗營養因子活性消失。試驗中，分別以乾式(乾燥後磨粉樣品)及濕式(直接濕磨為粉漿樣品)兩種方式預處理，再接續以酸熱、酵素或球磨處理。在乾式處理溫度包括45、90、135、及180℃，乾燥至水分含量約12-13%，以方便保存。結果顯示，以135及180℃乾燥者，有助於澱粉熱穩定結構的產生，經再熟製仍有最高含量之慢速消化澱粉(SDS)(D135:43%)及抗性澱粉(RS)(D180:27%)。當合併乾熱及酸熱 (0.1%酸/140℃) 處理3 h後，除了具特殊烤焙茶香氣外，其糊化溫度和熱焓值降低，顯示部分澱粉結晶結構在酸熱處理過程中被破壞，因而其eGI值降低，且此豆粉(AHDF, AHD135, AHD180)經再熟製過程，其eGI值仍明顯低於未經酸熱處理者(DF、D135、D180)。在濕式處理部分，當以pullulanase(0, 20, 40U/g starch) 去分支後，經冷卻澱粉回凝，RS顯著增加(SPu40: 40%)，但此結構對熱並不穩定。當以protease AN酵素水解澱粉粒外圍蛋白質後，豆粉糊液黏度提升並具成膠性，由光學顯微鏡觀察得知，包裹在澱粉外圍的蛋白質基質消失，但其膠體強度仍不足，且顆粒感明顯影響適口性。因此，後續需再以球磨處理。挑選溼式處理樣品(SPAN、S45及S90)、及乾式處理樣品(DF)，以行星式球磨機輾磨，以降低豆粉粒徑。當豆粉經球磨處理4及6 h後，豆粉平均粒徑大小皆降低至小於原本的一半，且溶解度顯著提高，糊液黏度則依樣品之不同，隨球磨時間有先下降再上升或逐漸下降之現象，但澱粉體外消化性質及eGI值稍微上升，且熟製後各組差異不大。經適度處理之紅豆水生產之副產物-水萃後紅豆粒因具有特殊性，可作為提供機能性(SDS及RS)之良好素材，應可提高其附加價值。以溼式處理及未經酵素處理(S90和90BM4H)或經酵素處理(SPAN和SPANBM4H)合併地瓜粉製成粉粿產品，豆粉的添加皆會使膠體硬度提升，SPAN系列比起S90系列尤其顯著，而當豆粉經過球磨則會使硬度降低，此外，隨豆粉取代比例的提高，內聚力及回復性變差，顯示樣品耐壓的能力降低。在所有樣品中，以S90BM4H豆粉取代25%膠體樣品之組成分地瓜粉，其性質最接近原始膠體樣品。

According to the 'Compendium of Materia Medica' and past studies, adzuki bean could not only reduce water retention in body but also contain a large amount of phytochemicals. Adzuki bean water contains special flavor that makes it sensation in the market. While generating adzuki bean water, a significant amount of by-products, blanched adzuki bean, will be left. The usage of the blanched adzuki bean is limited due to its light color and flavorless taste. Hence, blanched adzuki bean is inapplicable to make desserts such as traditional bean paste or sweet bean soup. Blanched Adzuki bean is used in animal food nowadays, although its main nutrients including starch and protein still remained. In order to increase the additional value of blanched adzuki bean flour to broaden its usage, the impacts of blanching on the morphology, physicochemical properties and digestibility of starch were discussed first. Then, some physical modifications were adopted to improve the functionality of blanched Adzuki bean flour, including dry heating, ball milling, acid-heat and enzymatic (pullulanase and protease) treatments. The composition, physicochemical properties, in vitro digestibility and estimated glycemic index (eGI) of the whole blanched adzuki bean flour were evaluated after those treatments. The purpose of this study is to obtain a treated flour with low eGI and/or good pasting properties by combining the treatments above eventually. The blanched adzuki bean lost 75% of total phenolics, inactivated the trypsin inhibitor completely and gelatinizated about 50% of starch. In addition, the decreases in paste viscosity, swelling power, solubility, and enthalpy were observed as well. Two types of treatment were carried on, including dry processing, which the dried blanched adzuki bean was ground followed by the modification, and wet processing, which the adzuki bean flour slurry was incubated with enzymes followed by drying. To reduce the moisture content of by-products for preservation, the blanched adzuki bean was oven-dried at various temperatures (45, 90, 135 and 180℃) until the moisture content of 12-13%. After drying at 135˚C and 180˚C, the dried adzuki bean flour had the highest SDS (43% in D135) and RS (27% in D180) contents. Furthermore, the combination of dry-heating (135 or 180℃) and acid-heat treatment (140˚C, 3 hr) led to an intense roasted tea odor, and an decreased starch digestibility and eGI value of the treated adzuki bean flour. This is due to the lower gelatinization temperature and lower enthalpy, resulting from a slight disruption of the ordered structure of starch after acid-heat treatment. In wet processing, starch digestibility altered after pullulanase treatment. SPu40 shows higher content of RS than SPu0, but the structure of RS was thermal unstable. The protease AN worked the best to remove the protein matrix surrounding the starch granules, thereby resulting in an increase in pasting viscosity and gel forming capability. The absence of protein matrix surrounding the starch granules was confirmed by optical microscopic images. Despite of these significant improvements, the gel from the modified adzuki bean flour was still weak and poor in palatability (gritty mouthfeel). Thus, the ball milling was then adopted to improve four selected, treated bean flours (SPAN, S45, S90 and DF). After being ball- milled for 4 and 6 h, the mean particle size of all bean flour reduced to smaller than half of its origin size. The ball-milled bean flour displayed an increased solubility and pasting properties were reduced or reduced and then increased depend on different sample. However, a slightly increased eGI value of ball-milled was determined after cooking. Overall, the results of this study showed that the blanched adzuki bean flour with appropriate treatments could modified its physicochemical properties and had potential for the adjunctive ingredient in food system providing SDS and RS. 0-50% of sweet potato starch were substituted by using the modified bean flour for sweet potato gel cake making. It showed that the addition of modified bean flour resulted in the increase of hardness and substitution of SPAN was more pronounced than S90. The hardness slightly decreased when ball milled bean flour was added. As substitution of modified bean flour increased from 0 to 50%, the decreased cohesiveness, resilience and compression resistant were recorded. Using 25% S90BM4H as substitution, the gel was most similar to control sample in all substitution groups.