摘要
为探究不同柑橘膳食纤维的性能差异及提高柑橘加工副产物综合利用率,利用酶解法制备4种柑橘(脐橙、苹果柚、沃柑、柠檬)皮渣膳食纤维,采用扫描电子显微镜、傅里叶变换红外光谱及X射线衍射对纤维形态结构进行表征,并测定理化性质及体外抗氧化活性,通过主成分分析评价不同柑橘纤维综合品质。结果显示,酶法制备的柑橘纤维性能存在品种差异,柠檬纤维总纤维含量(67.63±0.46)%最高,脐橙纤维组成比例最好,沃柑、脐橙纤维水合性能和体外抗氧化活性最强,苹果柚纤维在4种纤维中表现出最高表观黏度。综合评价从高到低排序为:脐橙纤维、沃柑纤维、苹果柚纤维、柠檬纤维。结果表明,酶法制备的4种柑橘膳食纤维均有较好生理活性,其中脐橙纤维综合品质最佳,作为食品添加剂有较广应用前景。
柑橘是世界第一大类水
膳食纤维因其在调节肠道菌
碱液浸提法因其提取率较高而常被用于膳食纤维提
因此,本研究选用橙类(脐橙)、宽皮柑橘(沃柑)、柠檬、柚(苹果柚)4种产量较高的柑橘作为原料,通过酶解柑橘皮渣制备膳食纤维,并对其理化性质及功能进行综合评价,以期为拓宽柑橘纤维应用范围、提高柑橘副产物综合利用率提供理论基础。
脐橙(Citrus sinensis (L.) Osbeck),购于湖南省邵阳市新宁县;柠檬(Citrus limon cv Fino),购于四川省资阳市安岳县;沃柑(Citrus reticulata),购于湖南省永州市武鸣县;苹果柚(Citrus maxima ‘Apple’),购于湖南省常德市澧县。果实均无损伤和腐烂。
将果实洗净后剥皮,皮渣于烘箱中60 ℃干燥48 h,粉碎后过孔径0.178 mm筛,将柑橘皮粉置于干燥器中保存备用。参照Liu
% | (1) |
采用扫描电镜仪(EVO LS10,德国Carl Zeiss公司)观察柑橘纤维微观结构;用红外光谱仪(Nicolet iS5,美国Thermo fisher scientific公司)、X射线衍射仪(D8 Advance,德国Bruker公司)及热重分析仪(NETZSCH STA 449 F3/F5 Jupiter,德国耐驰公司)分析柑橘纤维结构特性并计算结晶度,具体方法参考文献[
采用超纯水配制0.5%柑橘纤维悬浮液,用激光粒度分析仪(LS-POP VI,欧美克科技有限公司)测定粒径分布情况;用全自动色度分析仪(Color Quest XE,美国Hunter Lab公司)测定纤维色泽;参考GB 5009.88—2014测定总膳食纤维TDF、不可溶性膳食纤维IDF及可溶性膳食纤维SDF含量;参考刘岩
以DPPH·和ABT
参照万仁口
铁还原能力(FRAP)通常用于分析植物提取物的总抗氧化活性。FRAP测定方法:取0.1 mL待测纤维,加入3 mL预热至37 ℃的FRAP工作液,再加入2 mL超纯水,摇匀并于37 ℃水浴反应30 min。吸光度均采用紫外-可见分光光度计(UV-1800,苏州岛津仪器有限公司)测定。

图1 不同柑橘纤维的扫描电镜图(500×)
Fig.1 The SEM photograph of different citrus dietary fiber
A:脐橙纤维(NODF) Navel orange fiber; B:苹果柚纤维(APDF) Apple pomelo fiber; C:沃柑纤维(ODF) Orah fiber; D:柠檬纤维(LDF) Lemon fiber。下同The same as below.
不同柑橘膳食纤维的红外光谱如

图2 不同柑橘纤维的红外光谱图
Fig.2 FT-IR spectra of different citrus dietary fiber
如

图3 不同柑橘纤维的X射线衍射图
Fig.3 XRD of different citrus dietary fiber
不同柑橘纤维热稳定性如

图4 不同柑橘纤维的热重分析
Fig.4 Thermogravimetric analysis of different citrus dietary fiber
注: 同行不同小写字母表示组间存在显著性差异(P<0.05)。Note: There are significant differences between different lowercase letters in the same row(P<0.05).
不同柑橘膳食纤维的粒径分布如

图5 不同柑橘纤维的粒径分布
Fig.5 Particle size distribution of different citrus dietary fiber
由
通过酶法制备的4种柑橘纤维主要成分均为IDF,含量达50%以上。柠檬总膳食纤维(TDF)及IDF含量均最高,分别为67.63%和56.60%。脐橙SDF含量高于其他3种柑橘纤维,为14.06%,且IDF与SDF比例较好(3.6∶1),可能对其生理活性具有一定促进作用。
沃柑纤维的持水力在4种膳食纤维中最高;脐橙、苹果柚、沃柑纤维的持油力差异不显著,柠檬纤维的略低;4种纤维的溶胀性为14.17~20.00 mL/g,脐橙纤维溶胀性最高,其余3种纤维差异不显著。
如

图6 不同柑橘纤维的剪切应力(A)和黏度(B)
Fig.6 Shear stress(A) and viscosity (B) of different citrus dietary fiber
不同柑橘纤维黏度随剪切速率变化规律如
不同柑橘膳食纤维抗氧化活性如

图7 不同柑橘纤维的抗氧化活性
Fig.7 Antioxidant activity of different citrus dietary fiber
A:DPPH·清除率Scavenging effect of DPPH · radicals; B:ABT
如
将各指标测定值进行相关性分析,结果见
注: 相关性为Pearson类型; *表示显著相关(P<0.05); **表示极显著相关(P<0.01)。Note: The correlation is Pearson type; * indicates significant correlation (P<0.05); ** indicates extremely significant correlation (P<0.01).
进行主成分分析前,采用KMO检验对所获数据进行适应性检验,经计算得知KMO=0.646,大于0.5,因此,可进行主成分分析。如
由
以3个主成分分别对应的方差贡献率占累积方差贡献率的比例作权重建立综合评价模型:F=0.540F1+0.341F2+0.119F3,综合评价结果如
柑橘皮渣是膳食纤维的主要来源之一,利用酶法制备脐橙、苹果柚、沃柑及柠檬皮渣膳食纤维,并分析比较其理化、结构及抗氧化活性差异。通过结构解析发现,4种柑橘纤维的红外光谱均呈现纤维素特征吸收峰,为纤维素Ⅰ晶体构型,表明酶处理未改变柑橘纤维晶型。
膳食纤维水合作用对肠道内营养物质消化吸收有直接影响,可增加饱腹感,起预防肥胖的作用,其生理功能与其表面结构密切相关。本研究表明,在一定粒度范围内,纤维粒径越小,其持水力、持油力越高,这与Huang
研究表明柑橘皮渣可作为一种优质膳食纤维来源,为柑橘加工副产物综合利用提供新思路,提高柑橘加工链价值。本试验中制得4种柑橘纤维IDF占比均较大,未达到理想比例,仍需深入研究以改善SDF与IDF比例,进一步提升柑橘纤维的生理活性。
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