Effects of SH-containing Antioxidant and Atmosphere Modification on Quality and Shelf Life of Fresh-cut Carambola (Averrhoa carambola L.) Fruits.

• Main Authors: Chen-Chu Lu, 呂承祖
• Other Authors: 吳俊達
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/05745157864783349798

碩士 === 國立臺灣大學 === 園藝學研究所 === 100 === 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¬, 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.