含硫氫基抗氧化劑與改變大氣組成處理對截切楊桃之品質與櫥架壽命的影響

Abstract

楊桃（Averrhoa carambola L.）為酢醬草科（Oxalidaceae）五斂子屬多年生常綠性大灌木，在臺灣主要作為鮮食甜點消費，果實橫切面呈星形，適合作為水果盤、沙拉、盤飾，具有發展為截切產品潛力。由於楊桃截切後外果皮邊緣褐變相當快速，僅需2小時便能觀察到褐化現象，是影響楊桃品質劣變的主要問題。此外，截切楊桃組織受傷面積增加、組織液滲漏，導致微生物滋長，影響食品安全與櫥架壽命。目前國內關於截切楊桃產品保鮮技術的資料並不多，因此本論文試驗目的在探討抗褐化劑與改變大氣組成處理技術應用在截切甜味種楊桃產品保鮮及延長櫥架壽命的效益。 本試驗針對含SH基之抗氧化劑N-乙醯-L-半胱胺酸（N-acetyl-l-cysteine；NAC）、L-半胱胺酸（L-cysteine；Cys）與L-半胱胺酸鹽酸鹽（L-cysteine hydrochloride；CysH）應用於抑制截切‘紅龍’楊桃褐變之可能性與使用浸漬濃度，並添加到幾丁聚醣可食性被膜觀察其抑制褐化之相容性及對楊桃切片品質之影響。對照組截切‘紅龍’楊桃外果皮切邊L*值於5℃貯藏2天便明顯降低褐變。貯前以0.5% NAC溶液浸泡處理1分鐘之樣品能有效抑制切邊褐化至少達10天，其外果皮切邊L*值維持在50.6，與截切當日沒有明顯差異；再提高NAC濃度並無法增進抑制褐化效果。而CysH浸泡處理濃度0.7%以上對截切‘紅龍’楊桃L*值即具有顯著褐變抑制效果，其切邊L*值於貯藏第10天維持在57.9，且與截切當日L*值62.5無顯著差異。 楊桃切片貯藏於5℃ O2濃度5%以下氣調處理組後皆具抑制嗜溫好氧菌生長效果，貯藏第8日總生菌數便顯著低於對照組；至第10日O2濃度5%以下處理約在3.46~3.62 log CFU g-1，與對照組4.29 log CFU g-1差異明顯。黴菌及酵母菌之菌數各組間並無顯著差異存在，貯藏後第10日之黴菌及酵母菌含量約在5.03~5.11 log CFU g-1之間，超出法令安全標準而喪失商品價值。顯示真菌是楊桃切片汙染主要的微生物，0.5~12.9％O2濃度並不會對黴菌及酵母菌生長造成顯著抑制效果。 為釐清CO2於抑菌方面的效果，本試驗以O2濃度2%結合不同濃度的CO2進行調查，而黴菌及酵母菌菌數結果顯示，CO2濃度5%以上處理於5℃貯藏8日菌數約在4.05~4.23 log CFU g-1之間，與空氣處理組、2%O2+0%CO2處理組之4.47~4.62 log CFU g-1具有顯著性差異，2%O2+5%CO2處理於貯藏後16日由於生菌數5.08 log CFU g-1，櫥架壽命結束；2%O2+10%CO2、2%O2+15%CO2、2%O2+20% CO2處理則分別於貯藏後18、20日由於生菌數超標失去商品價值，而CO215%與20%間差異不顯著，且不會影響品質。15%以上CO2氣調處理貯後第2日便有顯著乙醛生成，其值3.75~5.21 μL L-1，與空氣處理組之值0.11 μL L-1有顯著差異；貯藏第8日2%O2+20%CO2處理乙醛生成更顯著高於2%O2+15%CO2組。而CO2高於5%處理組貯藏2日乙醇含量便高於空氣處理組，乙醇累積量與氣調環境CO2濃度成正比。由於2% O2 +15% CO2與2%O2 +20%CO2抑菌效果類似，且明顯優於其他處理組，而前者誘導乙醇及乙醛累積情況較後者輕微，因此判定2%O2+15%CO2為本試驗截切‘紅龍’楊桃最佳氣調貯藏條件。 以厚度100 μm低密度聚乙烯（LDPE）、700 μm聚丙烯（PP）袋分別盛裝150 g、300 g‘紅龍’楊桃切片，進行被動（passive）或主動（active）氣變包裝在5℃進行調查。被動包裝無論盛裝150 g或是300 g楊桃切片，因包裝內達到穩定氣體環境之速率較慢，無法達到O2 2 % + CO2 15%氣體組成，導致楊桃切片暴露於不適當的高O2濃度（>2%）/低CO2濃度（<15%）環境較久，無法發揮抑菌效果；主動包裝中盛裝150 g的楊桃切片，無論LDPE或PP袋皆無法維持理想的氣體環境，而盛裝300 g的LDPE、PP袋內平均氣體濃度分別為3.53%O2 + 12.67%CO2 與5.11%O2 + 13.97%CO2，皆可延長截切楊桃壽命由8日至14日，兩組於抑菌效果、乙醛及乙醇生成皆無顯著差異，故選用較接近目標氣體濃度之LDPE袋與CysH結合，觀察是否具有同時抑菌及抑制褐化發生之效果。 截切‘紅龍’ 與‘馬來西亞8號’楊桃貯前浸泡1% CysH溶液1分鐘，以厚度100 μm LDPE袋進行O2 2% + CO2 15%主動氣變包裝處理，在5℃評估櫥架壽命。兩品種楊桃切片外果皮切邊L*值在整個貯藏期間並無顯著下降，維持在60左右，於貯藏2日起便與對照組出現顯著差異。抑制微生物生長方面，於‘紅龍’與‘馬來西亞8號’皆由於經主動氣變包裝處理，而延長櫥架壽命，主動氣變包裝使‘紅龍’楊桃黴菌及酵母菌數超出5 log CFU•g-1法訂標準日期由10日延長至16日；‘馬來西亞8號’楊桃則由8日延長至12日。CysH貯前浸泡處理加上O2 2% + CO2 15%主動氣變包裝技術，可同步解決褐變及微生物滋長兩大楊桃切片劣變問題，值得截切楊桃保鮮處理作業之參考。

The carambola (Averrhoa carambola L.) is a large evergreen shrub belonging to Oxalidaceae. In Taiwan the fruit is primarily marketed for fresh consumption and has great potential as a fresh-cut produce. Tissue discoloration is the most important factor in the deterioration of fresh-cut starfruit. Browning of the cut surface around the exocarp occurs rapidly and is evident as early as 2 h after cutting. Sap released from the cut surface also renders the produce susceptible to microbial contamination, thus raising concerns about food safety and affecting its shelf life. Little information is currently available about the postharvest technology of fresh-cut starfruit. This thesis devotes to investigations on the use of anti-browning agent and atmosphere modification for prolonging the shelf-life of fresh-cut sweet cultivar of starfruit. The feasibility of using anti-browning agents containing SH functional group, namely N-acetyl-l-cysteine (NAC), L-cysteine (Cys), and L-cysteine hydrochloride (CysH) to inhibit browning in fresh-cut ‘Hong Long’ starfruit was studied. Experiments were conducted to investigate the effective concentrations of these agents for use in immersion treatments, as well as the effect of incorporating them into chitosan edible film on the browning and quality of starfruit slices. Control treatment comprises storing slices of ‘Hong Long’ starfruit at 5℃. The L* value around the exocarp of cut surface decreased markedly in control after 2 d and browning was observed. Immersing the slices in 0.5% NAC for 1 min before storage effectively inhibited browning for at least 10 d, and resulted in L*value of 50.6 around the exocarp of cut surface, which was not significantly different from that obtained immediately after cutting. Increasing NAC concentration beyond 0.5% did not increase the anti-browning effect. Immersion in solutions containing 0.7% CysH or higher significantly inhibited browning, and resulted in L*value of 57.9 around the exocarp of cut surface after 10 d of storage, which was not significantly different from the L* value of 62.5 obtained on the day of cutting. Controlled atmosphere containing 5% oxygen (O2) inhibited the growth of mesophilic aerobic microbes on starfruit slices stored at 5℃, where the total viable count was lower on Day 8 of storage compared with control. On Day 10, total viable count in controlled atmosphere treatments containing 5% O2 or lower ranged 3.46-3.62 log CFU g-1, which was significantly lower than 4.29 log CFU g-1 in control. There was no difference among treatments in the viable count of molds and yeasts with total counts of these ranging 5.03-5.11 log CFU g-1 on Day 10 of storage, which was beyond the safety limit allowable by law and rendered the product unmarketable. This shows that fungi are the main factor in the microbial contamination of starfruit slices. Oxygen concentrations of 0.5-12.9% did not inhibit molds and yeasts significantly. To investigate the inhibitory effect of carbon dioxide on microbes, different carbon dioxide concentrations were provided for storage while maintaining 2% oxygen. Carbon dioxide (CO2) concentration of 5% or higher at 5℃ resulted in mold and yeast combined count range of 4.05-4.23 log CFU g-1 on Day 8 of storage, which was significantly lower than 4.47-4.62 log CFU g-1 obtained with storage in air and 2% O2+0% CO2. Starfruit slices in the 2% O2+5% CO2 treatment reached the end of their shelf life on Day 16 because total viable count reached 5.08 log CFU g-1. The ends of shelf life in the 2% O2+10% CO2, 2% O2+15% CO2, and 2% O2+20% CO2 treatments were 18, 20, and 20 days after storage, respectively, upon which the total viable count exceeded the allowable limit and the produce became unmarketable. No difference in shelf life and quality was observed between 15% and 20% CO2 treatments. Carbon dioxide concentration of 15% or higher resulted in significant acetaldehyde production, ranging 3.75-5.21 μL L-1 on Day 2 after storage. Meanwhile acetaldehyde concentration was only 0.11 μL L-1 in the air treatment. Acetaldehyde production was significantly different between the 20% and 15% CO2 treatments 8 d after storage. On Day 2 of storage, higher levels of ethanol were present in treatments with CO2 concentrations of 5% and higher compared with the air treatment. There was positive correlation between accumulation of ethanol and CO2 concentration in the storage atmosphere. The 2% O2+15% CO2 and 2% O2+20% CO2 treatments inhibited microbial growth to a similar extent and were superior to other treatments in this respect, while accumulation of acetaldehyde and ethanol was induced to a lesser extent in 2% O2+15% CO2. Therefore, it is concluded that 2% O2+15% CO2 is the optimal controlled atmosphere condition for storage of fresh-cut ‘Hong Long’ starfruit. Passive or active modified atmosphere conditions at 5℃ were investigated by packing 150 g or 300 g of sliced ‘Hong Long’ starfruit in 100 μm LDPE and 700 μm PP packaging. Passive packaging could not attain O2 2 % + CO2 15% either with 150 g or 300 g starfruit slices due to slow attainment of stable gaseous environment. Therefore with passive packaging the starfruit slices were exposed to undesirably high O2 level (>2%) and low CO2 level (<15%) for a longer period and thus microbial growth was not inhibited effectively. With active packaging, an ideal gaseous environment could not be attained by 150 g starfruit slices either when LDPE or PP bags were used. However, active packaging of 300 g starfruit slices in LDPE and PP bags resulted in 3.53%O2 + 12.67%CO2 and 5.11%O2 + 13.97%CO2&not;, respectively and increased the shelf life of the fresh-cut starfruit from 8 d to 14 d, with no significant difference in microbial growth inhibition and production of acetaldehyde and ethylene between the two types of bags used. However since LDPE packaging resulted in gaseous condition closer to the target concentrations, it was combined with CysH dipping treatment to investigate whether microbial growth and tissue discoloration could be inhibited simultaneously. Dipping treatment of 1% CysH was combined with active modified atmosphere packaging in 100 μm LDPE bags injected with O2 2% + CO2 15% to study their effects on the shelf life at 5℃ of the cultivars ‘Hong Long’ and ‘Malaysia’ starfruit. In both cultivars L* values around the exocarp of cut surface did not decrease significantly throughout the storage period; the values remained at approximately 60 and became significantly different from control after 2 d of storage. Modified atmosphere packaging also increased the shelf life of both cultivars, whereby in ‘Hong Long’ the time taken for mold and yeast count to exceed the 5 log CFU•g-1 allowable limit was lengthened from 10 d to 16 d, whereas in ‘Malaysia’ it was lengthened from 8 d to 12 d. Combining 1% CysH dipping treatment before storage with O2 2% + CO2 15% active modified atmosphere packaging could solve both browning and microbial growth, which are the two main deterioration factors in fresh-cut starfruit, and therefore serves as a valuable reference for the postharvest procedure of this produce.