基于GC-MS分析短波紫外线处理采后香蕉挥发性组分

应用正交试验优化顶空固相微萃取(HS-SPME)萃取条件,研究经UV-C处理的采后香蕉挥发性组分的变化。通过单因素测定合适的萃取头、萃取前的超声时间、样品量和萃取温度,再利用正交试验获得SPME最佳的萃取参数。在此基础上,测定和鉴定UV-C处理组和对照组香蕉果肉的挥发性化合物,比较两者挥发性成分的差异,评价UV-C处理采后香蕉的香气效果。结果表明,最佳萃取参数为:超声时间20 min、样品量4.0 g、萃取温度50℃,在此条件下鉴定出两组香蕉果肉挥发性组分共169个,主要由酯、醛、酮、醇和其他组成,其中酯类有58个、醛类有34个、酮类有27个、醇类有17个、其他类有33个,UV-C组的总酯含量(76.61%±0.25%)高于对照组的总酯含量(75.98%±0.39%)。两组香蕉的差异代谢挥发性组分共有38个,其中含量下调的有34个,含量上调的有4个。综上分析,采后香蕉经UV-C处理,其挥发性组分会受到影响,但其特征酯类和总酯含量略有提高。香蕉的香气主要源于酯类,UV-C处理进行香蕉贮藏保鲜不仅不会造成香蕉香气下降,反而会使其香气略有增强。     

Chemical Control of Ripening in Banana

A post-harvest dip of banana (Musa paradisiaca L.) fruits into the aqueous solutions of abscisic acid and indoleacetic acid significantly hastened the banana ripening, judging from increases in total sugars, acidity, ascorbic acid and units of von Losecke's colour chart during storage at 20°C. The treatment of bananas with gibberellic acid and kinetin, on the contrary, retarded banana ripening as indicated by higher values for firmness, starch, cellulose and hemicellulose. The results obtained suggest that ripening of banana can be controlled chemically.     

The onset of starch degradation during banana ripening is concomitant to changes in the content of free and conjugated forms of indole-3-acetic acid

Banana (Musa acuminata AAA cv. Nanicão) slices were infiltrated with mannitol (control) and mannitol plus indole-3-acetic acid (IAA); then, some important ripening parameters like starch degradation, synthesis of ethylene and respiration were monitored. The contents of free-IAA and conjugated forms of IAA (ester and amide) were analyzed, by GC-MS-SIM, throughout the ripening in both banana slices and whole bananas. The starch degradation of IAA-treated slices was delayed for several days, but there was no difference between control and IAA-treated slices in the ethylene and respiration profiles. On day zero after infiltration, free-IAA levels were 500-fold higher in IAA-treated slices than in the control slices, but within 72 hours they declined to values 15-fold higher than those in the control group, with concomitant increase in IAA-ester. Similar to the banana slices, the onset of starch degradation occurred in whole bananas only when the free-IAA concentration was about 4 ng/g FW. The results herein suggest that IAA levels play a role during banana ripening in events like starch degradation with the consequence of banana sweetening.     

Relationship between Ripening and the Development of Banana Anthracnose Caused by Colletotrichum musae (Berck. and Curt.) Arx

Wound anthracnose caused by Colletotrichum musae is the main disease affecting the quality of export bananas from the French Antilles. Little is known about the effects of ethylene on the development of wound anthracnose and quiescent anthracnose. The results of our experiments with 1‐methylcyclopropene (1‐MCP), an ethylene receptor site inhibitor, clearly revealed that ethylene was not directly involved in triggering rot development. Quiescent anthracnose symptoms were found to appear only after bananas began ripening. In contrast, wound anthracnose developed just as quickly in ‘green 1‐MCP‐treated bananas’ as in ‘yellow ripening bananas’. In cases of wound anthracnose, contrary to quiescent anthracnose, rot development was not dependent on the extent of peel ripeness.     

Differential Colonization Patterns of Bananas (Musa spp.) by Physiological Race 1 and Race 4 Isolates of Fusarium oxysporum f.sp. cubense

Fusarium oxysporum f.sp. cubense (Foc) is the causative agent of Fusarium wilt of bananas (Musa spp.). To clarify the colonization patterns of Foc in bananas, two green fluorescent protein‐tagged isolates, NT320 (race 1) and B2‐gfp (race 4), were used to follow infection of the banana varieties Pisang Awak and Brazil. Penetration and colonization of both isolates in roots of these two banana varieties were observed within 6 days, but sporulation in xylem vessels was not observed until day 30 postinoculation. Interestingly, B2‐gfp penetrated into xylem vessels of Pisang Awak banana roots more quickly than NT320, implying that the race 4 isolate is more virulent than the race 1 isolate. This result was further confirmed by comparing the disease severity of plants inoculated with NT320 with that of plants inoculated with B2‐gfp. Quantitative real‐time PCR revealed that some pathogenicity‐associated genes, including Fga1, Fhk1, Fow2 and Ste12, were upregulated by B2‐gfp during exposure to Brazil bananas, while they were either downregulated by NT320 or not significantly changed. These data might partly explain why the race 4 isolate was more virulent than the race 1 isolate.     

苹果果实香气产生过程中氨基酸和脂肪酸含量及一些相关酶活性的变化

研究了苹果果实成熟期间香气和乙烯的产生动态,以及游离氨基酸、游离脂肪酸含量和脂氧合酶(LOX)、醇-酰基转移酶(AAT)活性的变化.结果表明,果实香气物质是随着乙烯释放的增加而产生和增加的.在此过程中,异亮氨酸大量积累.游离脂肪酸在果实香气很少时呈增加趋势;随着香气产生的增多而迅速下降;乙烯高峰过后又有增加.脂氧合酶活性随着果实成熟而提高,其活性在乙烯释放达到高峰时达到最大值,之后迅速下降.醇-酰基转移酶活性在果实开始产生香气时迅速增加,之后保持较高活性.     

Identification and expression analysis of four 14-3-3 genes during fruit ripening in banana (<Emphasis Type="Italic">Musa acuminata</Emphasis> L. AAA group,cv. Brazilian)

To investigate the regulation of 14-3-3 proteins in banana (Musa acuminata L. AAA group, cv. Brazilian) fruit postharvest ripening, four cDNAs encoding 14-3-3 proteins were isolated from banana and designated as Ma-14-3-3a, Ma-14-3-3c, Ma-14-3-3e, and Ma-14-3-3i, respectively. Amino acid sequence alignment showed that the four 14-3-3 proteins shared a highly conserved core structure and variable C-terminal as well as N-terminal regions with 14-3-3 proteins from other plant species. Phylogenetic analysis revealed that the four 14-3-3 genes belong to the non-ε groups. They were differentially and specifically expressed in various tissues. Real-time RT-PCR analysis indicated that these four genes function differentially during banana fruit postharvest ripening. Three genes, Ma-14-3-3a, Ma-14-3-3c, and Ma-14-3-3e, were significantly induced by exogenous ethylene treatment. However, gene function differed in naturally ripened fruits. Ethylene could induce Ma-14-3-3c expression during postharvest ripening, but expression patterns of Ma-14-3-3a and Ma-14-3-3e suggest that these two genes appear to be involved in regulating ethylene biosynthesis during fruit ripening. No obvious relationship emerged between Ma-14-3-3i expression in naturally ripened and 1-MCP (1-methylcyclopropene)-treated fruit groups during fruit ripening. These results indicate that the 14-3-3 proteins might be involved in various regulatory processes of banana fruit ripening. Further studies will mainly focus on revealing the detailed biological mechanisms of these four 14-3-3 genes in regulating banana fruit postharvest ripening.     

Respiratory Contribution of the Alternate Path during Various Stages of Ripening in Avocado and Banana Fruits

The respiration of fresh slices of preclimacteric avocado (Persea americana Mill. var. Hass) and banana (Musa cavendishii var. Valery) fruits is stimulated by cyanide and antimycin. The respiration is sensitive to m-chlorobenzhydroxamic acid in the presence of cyanide but much less so in the presence of antimycin. In the absence of cyanide the contribution of the cyanide-resistant pathway to the coupled preclimacteric respiration is zero. In uncoupled slices, by contrast, the alternate path is engaged and utilized fully in avocado, and extensively in banana. Midclimacteric and peak climacteric slices are also cyanide-resistant and, in the presence of cyanide, sensitive to m-chlorobenzhydroxamic acid. In the absence of uncoupler there is no contribution by the alternate path in either tissue. In uncoupled midclimacteric avocado slices the alternate path is fully engaged. Midclimacteric banana slices, however, do not respond to uncouplers, and the alternate path is not engaged. Avocado and banana slices at the climacteric peak neither respond to uncouplers nor utilize the alternate path in the presence or absence of uncoupler.

The maximal capacities of the cytochrome and alternate paths, V_cyt and V_alt, respectively, have been estimated in slices from preclimacteric and climacteric avocado fruit and found to remain unchanged. The total respiratory capacity in preclimacteric and climacteric slices exceeds the respiratory rise which attends fruit ripening. In banana V_alt decreases slightly with ripening.

The aging of thin preclimacteric avocado slices in moist air results in ripening with an accompanying climacteric rise. In this case the alternate path is fully engaged at the climacteric peak, and the respiration represents the total potential respiratory capacity present in preclimacteric tissue. The respiratory climacteric in intact avocado and banana fruits is cytochrome path-mediated, whereas the respiratory climacteric of ripened thin avocado slices comprises the alternate as well as the cytochrome path. The ripening of intact fruits is seemingly independent of the nature of the electron transport path.

Uncouplers are thought to stimulate glycolysis to the point where the glycolytic flux exceeds the oxidative capacity of the cytochrome path, with the result that the alternate path is engaged.

     

Banana harvest maturity and fruit position on the quality of ripe fruit

There is an increasing market demand for smaller banana fruit. The way that this is being addressed involves harvesting some fruits on a bunch at a less advanced stage of maturity. Experiments were carried out to investigate the effect of age of fruit at harvest, position of the fruit on the bunch and different banana varieties on the speed of ripening and the quality of the ripe fruit at two different ripening temperatures after being exposed to exogenous ethylene. The maturity of bananas at harvest affected both the speed of ripening and the quality of the ripe fruit. Speed of ripening of fruit at 13°C was slower the more immature the fruit at harvest, but there was no effect on the speed of ripening of harvest maturity at a ripening temperature of 16°C. The effects of harvest maturity and position of the fruit on the bunch on peel colour and texture were significant but so small that they would be unlikely to affect the consumers' perception in a commercial situation. The higher soluble solids, flavour, sweetness and acceptability after ripening of the more mature fruit at harvest was sufficiently high that consumers could probably detect them.