摘要
为降低非浓缩还原(not from concentrate,NFC)橙汁储运销成本并提高其贮藏品质,以长叶香橙为原料,脱气杀菌后分别灌装至玻璃(glass,GL)、聚丙烯(polypropylene,PP)和聚乙烯(polyethylene,PE)(透氧率:GL<PP<PE)材质的包装中,25 ℃下避光贮藏并定期测定溶解氧(dissolved oxygen,DO)含量和相关品质指标。结果显示,DO值变化速度与包装材料的透氧率差异一致,GL、PP和PE中的还原糖含量均先降后升,可接受感官品质的贮藏时间分别为60、15和7 d,VC含量和色泽指标(∆E,A420)均与包装的透氧率呈极显著相关(P<0.01),类黄酮和酚酸化合物含量与包装透氧性不具有显著相关性。GL瓶中橙汁DO值在120 d内稳定在0.5 mg/L左右,其橙汁贮藏效果最佳。结果表明,在贮藏期间将DO值控制在0.5 mg/L及以下可更好地保持NFC橙汁的品质,实现NFC橙汁的常温储运。
柑橘类水果中含有黄烷酮、酚酸、柠檬苦素、L-抗坏血酸、类胡萝卜素、挥发性萜烯等多种生物活性化合物,具有抗氧
科研人员大多仅研究新型包装材料对橙汁品质的影响,如纸铝塑复合包
本研究采用不同透氧性的包装材料灌装橙汁,观察常温贮藏过程中溶解氧(dissolved oxygen,DO)含量的动态变化,研究其变化与橙汁贮藏品质的关系,从而明确NFC橙汁常温贮藏中DO值控制参数,为实现NFC橙汁的常温贮藏、延长其货架期、降低储运成本提供新思路。
长叶香橙(Citrus sinensis (L.) Osbeck),2019年3月采摘于西南大学柑桔研究所果园。
Pertifilm TM 测试片(菌落总数、金黄色葡萄球菌、大肠菌群、霉菌/酵母菌)购于3M 中国有限公司;NaOH、酚酞、邻苯二甲酸氢钾、草酸等试剂均为化学纯,购于重庆川东化工有限公司;冰乙酸、甲醇等为色谱纯,购于美国Sigma-Aldrich公司。
玻璃(glass,GL)瓶,购于徐州聚霖玻璃制品有限公司;聚丙烯(polypropylene,PP)瓶,购于河北沧州东盛塑料有限公司;聚乙烯(polyethylene,PE)蒸煮袋,购于河北保定龙兴包装有限公司。
GL、PP和PE均为无色透明材料,各包装材料的性能见
注: “—”表示透氧率低于最低检测限,无法检测;“*”该数据引自文献[
S9溶氧仪,梅特勒托利多(上海)有限公司;Color i5色差仪,瑞士Gretag Macbech公司;TU-1901紫外-分光光度计,普析通用仪器有限责任公司;WAY-2S阿贝折光仪,上海精密科学仪器有限公司; 1260 infinity高效液相色谱仪(HPLC-DAD),安捷伦科技(中国)有限公司。
长叶香橙鲜果于西南大学柑桔研究所中试车间内经清洗、分级、压榨、精滤、真空脱气后,在杀菌管道内进行巴氏杀菌(95 ℃,30 s),然后在灌装室内取样至无菌操作台,立即分别热灌装至灭菌的GL瓶、PP瓶、PE蒸煮袋(透氧性:GL<PP<PE)中,灌装至顶空空隙小于0.1 cm,密封,冷水浴中冷却至室温,最后放置在恒温培养箱中,于25 ℃(模拟室温)下用多层黑色塑料膜包裹避光贮藏。所有样品准备2个平行,每个样品重复测定3次,分别在第0、3、7、15、30、60和120 天时取样测定,当感官评定总分低于50分的样品不再进行理化指标测定。以第0天的橙汁样品作为空白对照样品。
1)感官评定。参照GB/T 16291.2—2010《感官分析:选拔、培训和管理评价员一般导则:第二部分:专家评价员》的要求对小组成员进行培训,要求评定人员对标准橙汁的感官属性非常熟悉。感官评价指标为色泽、气味、滋味和状态与杂质,评定时均采用10分制,8~10分为标准,5~7分为合格,0~4分则为不合
2)溶解氧(DO)测定。使用S9溶氧仪进行侵入型测定,测定前对溶氧仪进行两点校准,校准结束后在氮气环境中测定样品,测定时轻微晃动溶氧仪,每个样品测定5次。
3)色泽的测定。 Color i5色差仪开机后选择光源C-02, 设定测试参数
4)褐变度(A420)的测定。国内外通常用A420作为果汁非酶褐变的指标,主要是因为非酶褐变反应所产生的色素在420 nm处有非常强的吸光值,吸光值越大,褐变就越严
5)还原糖含量的测定。 根据行业标准NY/T 2742—2015《水果及制品可溶性糖的测定 3,5-二硝基水杨酸比色法》进行测定。 以葡萄糖为标准品, 根据标准中的方法制作标准曲线, 所得回归方程:y=0.0491x+0.0074,式中y为质量浓度,x为吸光度,
6)抗坏血酸(VC)的测定。根据GB 5009.86—2016《食品安全国家标准 食品中抗坏血酸的测定》第三法——2,6-二氯靛酚法进行测定,结果以每100 g橙汁所含L-抗坏血酸质量表示(mg/100 g)。
7)类黄酮化合物(芦丁、橙皮苷和香蜂草苷)的测定。 称取2份平行试样6 g于50 mL离心管中, 加入8 mL乙酸乙酯, 涡旋混匀5 min, 于8 000 r/min条件下离心10 min,收集上清液,重复上述操作1次,合并上清液,氮吹浓缩至干,50%甲醇溶液定容至2 mL,经0.22 μm微孔有机滤膜过滤后,高效液相色谱仪进样20 μL进行检测。将芦丁、橙皮苷和香蜂草苷标准品配制成不同浓度梯度的混合溶液上机检测,制得3种类黄酮化合物的标准曲线回归方程,见
8)酚酸类化合物(阿魏酸、对香豆酸和咖啡酸)的测定。称取2份平行试样6 g于50 mL离心管中,加入5 mL 8 mol/L的NaOH溶液,涡旋混匀反应1 h; 8 mol/L的HCl调节pH至2.0,加入8 mL乙酸乙酯和甲基叔丁基醚(体积比1∶1)混合液,于10 000 r/min条件下离心10 min,收集上清液,重复上述操作1次,合并上清液,氮吹浓缩至干,50%甲醇溶液定容至2 mL,经0.22 μm微孔有机滤膜过滤后,高效液相色谱仪进样20 μL进行检测。将阿魏酸、对香豆酸和咖啡酸标品配制成不同浓度梯度的混合溶液上机检测,制得3种酚酸化合物的标准曲线回归方程,见
9)微生物检测方法。菌落总数的检测参照《3M Pertrifilm TM菌落总数测试片法》进行检测。大肠菌群的检测参照《3M Pertrifilm TM大肠菌群测试片法》进行检测。霉菌及酵母菌的检测参照《3M Pertrifilm TM霉菌及酵母菌测试片法》进行检测。金黄色葡萄球菌的检测参照《3M Pertrifilm TM金黄色葡萄球菌测试片法》进行检测。以上微生物检测在NFC橙汁冷藏结束(180 d)时进行。目前国标对于NFC果汁的微生物指标没有明确规定,所以根据GB 7101-2015《食品安全国家标准 饮料》和GB 29921—2013《食品安全国家标准 食品中致病菌限量》等标准,将对NFC橙汁中的微生物进行严格控制。
由

图1 不同包装材料中DO值的变化
Fig.1 Changes of dissolved oxygen content in different packaging materials
图

图2 GL(A)、PP(B)、 PE(C)包装橙汁感官指标评分雷达图
Fig.2 Orange juice sensory index score radar chart of GL(A),PP(B) and PE(C)

图3 不同包装的橙汁的感官评价总分
Fig.3 Orange juice sensory evaluation score of GL,PP and PE
由
注: 不同小写字母表示同一指标在两组样品间存在显著差异。Note: Different lower letters indicate the significant difference between the two groups of samples.
由

图4 贮藏过程中褐变度(A420)的变化
Fig. 4 Changes of browning index (A420) during storage

图5 贮藏过程中还原糖含量的变化
Fig.5 Changes of reducing sugar content during storage
在有氧条件下,VC发生有氧降解形成脱氢抗坏血酸,经一系列反应后最终生成还原酮,还原酮再参与美拉德反应生成黑褐色物质;在无氧条件下VC也会发生降解,但速度比有氧降解慢。

图6 贮藏过程中VC含量的变化
Fig.6 Changes of VC content during storage
为探究不同DO值变化对橙汁中类黄酮化合物的影响,以含量较为丰富的橙皮苷、芦丁和香蜂草苷为代表进行分析,结果如

图7 贮藏过程中橙皮苷(A)、芦丁(B)和香蜂草苷(C)含量的变化
Fig.7 Changes of the contents of hesperidin (A),rutin (B) and didymin (C ) during storage
为了探究橙汁贮藏过程中DO值对酚酸化合物的影响,选择以占比相对较多的阿魏酸、咖啡酸和对香豆酸为代表进行测定,其结果如

图8 贮藏过程中阿魏酸(A)、对香豆酸(B)和咖啡酸(C)含量的变化
Fig.8 Changes of ferulic acid (A),p-coumaric acid (B) and caffeic acid (C) during storage
橙汁中DO值过高,不仅会引起营养物质发生氧化降解,还有助于好氧菌的生长繁殖,加速橙汁风味和营养品质劣
VC降解速率可通过动力学模型进行定量描述,降解速率常数K的绝对值越小,表明降解速率越慢。通过分析发现,3种不同包装中的VC降解均符合一级降解动力学模型,GL、PP和PE包装中Vc的降解速率常数K分别为-0.057 4±0.002、-1.271 8±0.001和-1.224 7±0.006,说明GL包装中VC的降解速率最慢,该结果与Wibowo
通过进一步分析发现,橙皮苷的减少量最大,其次是芦丁,香蜂草苷最少,出现该现象除与橙汁中黄酮化合物本身的含量有关外,由于黄酮类化合物结构中常含有酚羟基、甲基、甲氧基等取代基团,酚羟基的甲基化或糖基化会都降低柑桔酚类物质的自由基清除能力,而且自由羟基所含数目与抗氧化能力呈显著正相
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