Johnston Carol S, Bowling D L
Department of Nutrition, Arizona State University East, Mesa 85212, USA.
J Am Diet Assoc. 2002 Apr;102(4):525-9. doi: 10.1016/s0002-8223(02)90119-7.
To compare the vitamin C content of reconstituted frozen orange juice concentrates at preparation to that of ready-to-drink orange juices purchased 4 to 5 weeks from expiration.
Juices were unsealed and analyzed for reduced and oxidized vitamin C content at the time of purchase and reanalyzed 3 times weekly for 4 to 5 weeks. Same-lot samples of the ready-to-drink juices remained sealed after purchase and were opened for analyses at 3, 2, 1, or 0 weeks before expiration. SAMPLES/SETTING: Orange juices were reconstituted frozen concentrates, ready-to-drink juice packaged in resealable, screw-top containers, or ready-to-drink juice packaged in nonresealable containers. Juices were obtained from local retailers and stored at 4 degrees C in their original containers when appropriate.
The reduced vitamin C content of juices analyzed repeatedly, 3 times weekly for 4 weeks, were compared using repeated measures analysis of variance. Linear regression lines were computed for reduced vitamin C in each juice over time, and differences between slopes were analyzed by oneway analysis of variance.
The orange juices from frozen concentrates contained 86 mg reduced vitamin C per fluid cup at initial preparation and 39 to 46 mg/c after 4 weeks of storage. Ready-to-drink juices averaged significantly lower reduced vitamin C: 27 to 65 mg/c at opening and 0 to 25 mg/c at expiration 4 weeks later. Ready-to-drink orange juices had twofold to threefold higher concentrations of oxidized vitamin C vs the orange juices reconstituted from frozen, and the decomposition rate of reduced vitamin C was similar for all juices, about 2% per day once opened.
Ready-to-drink orange juices should be purchased 3 to 4 weeks before expiration date and consumed within 1 week of opening.
比较复原后的冷冻浓缩橙汁在制备时的维生素C含量与距过期还有4至5周时购买的即饮橙汁的维生素C含量。
果汁开封后在购买时分析还原型和氧化型维生素C含量，并在4至5周内每周分析3次。购买后，即饮果汁的同批次样品保持密封，并在过期前3周、2周、1周或0周开封进行分析。
样本/环境：橙汁为复原后的冷冻浓缩液、包装在可重新密封的螺旋盖容器中的即饮果汁或包装在不可重新密封容器中的即饮果汁。果汁购自当地零售商，并在合适的情况下在原容器中于4℃储存。
对每周分析3次、持续4周的果汁的还原型维生素C含量进行重复测量方差分析。计算每种果汁中还原型维生素C随时间变化的线性回归线，并通过单因素方差分析分析斜率之间的差异。
冷冻浓缩橙汁在初始制备时每液杯含有86毫克还原型维生素C，储存4周后为39至46毫克/杯。即饮果汁的还原型维生素C平均含量显著较低：开封时为27至65毫克/杯，4周后过期时为0至25毫克/杯。即饮橙汁的氧化型维生素C浓度比冷冻复原的橙汁高2至3倍，所有果汁中还原型维生素C的分解速率相似，开封后每天约2%。
即饮橙汁应在过期前3至4周购买，并在开封后1周内饮用。
