The purpose of this study was to investigate the effect of various types of wax-coatings, and container liners on the physicochemical characters of Pakistani mandarins (Feutrellt's Early-and Kinnows) during postharvest storage at ordinary room conditions. Changes in citrus volatiles and free amino acids were studied to test their suitability as chemical quality/senescence indices and correlations between physico chemical and organoleptic characters of mandarins were also computed. Literature pertaining to fresh citrus fruits external (rots, physiological disorders, blemishes) and internal (total soluble solids (TSS), acid, TSS/acid, juice content, volatiles, free amino acids) quality characters was surveyed. Preharvest and harvest factors (rootstock, tree condition, soil, climate, weather, production area, harvesting season, garden treatments (water management, fertilizers, pesticides, fungicides, growth regulators, colour enhancer, internal quality modifier) ,picking methods and postharvest treatments(washing, grading, degreening, precooling, curing, conditioning, decay control techniques (fungicides, fumigation, growth regulators, heat treatment, irradiation, citrus volatiles), controlled atmosphere storage, waxing, packaging, container lining, packing, containerization) affecting the postharvest quality and storage behaviour of citrus fruits have been reviewed.
Effect of various postharvest treatments was studied in five citrus crops (1976-77,1977-78,1979-80,1982-83,1983-84) in early, mid and late season harvests. Feutrell's were picked in November, December and January whereas kinnows were procured in January, February, March and April. The salient features of these findings are summarized below: Polyethylene (PE) lining (0.030 mm) was the most effective treatment followed by waxing (with Fruitex, Britex561 and Seal Britex-56) and cellophane lining (0.030 mm) for reducing weight loss of both the mandarins during storage at room conditions as compared to newspaper lining (0.093 mm), but waxpaper lining (0.024 mm) had no such effect. Even in severe storage conditions (23-360C, 47.0-76.5 % RH) these treatments were effective in retarding moisture loss from citrus fruits. There did not seem to be any relationship between weight loss and time of picking in both the cultivars, however, weight loss seemed to be closely related to the conditions of storage environment (temperature, humidity). Behaviour of Feutrell's Early and kinnow mandarins was almost similar during postharvest storage as for as weight loss was concerned.
Wax-coatings of various types and different container liners had no significant effect on internal quality characters like ascorbic acid, acidity and sugar/acid ratio of both the mandarins during postharvest storage at room conditions. Waxed mandarins of both the cultivars in some harvests contained less sugar than that of control fruits; however, this effect of waxing on sugar contents was inconsistent and variable. As for as the effect of storage was concerned, there was significant decrease in acidity and ascorbic acid and significant increase in reducing, non reducing, total sugars and sugar/acid ratio decrease in sugar contents during storage could be mainly 1ue to time of picking and postharvest storage temperatures.
Ascorbic acid and acidity contents were higher in early picked Feutrell's Early and kinnow mandarins whereas sugar contents and sugar/acid ratios were higher in late picked fruits. Changes in chemical constituents of early and late picked Feutrell's early mandarins during storage were almost comparable. Decrease in ascorbic acid and acidity was comparable in early and late picked kinnows but the changes in sugar con tents were variable. Decrease in sugar contents during age of late picked kinnows could be due to two reasons. Changes which were to start in storage might have commenced on the tree and high postharvest storage temperature (23-36°0) might have caused abnormal respiration. Feutrellts Early mandarins contained more ascorbic acid than kinnows, but acidity, sugars and sugar/acid ratio were higher in kinnows.
Regression analysis studies indicated that correlations between external quality characters (external appearance and firmness) and weight loss of control and treated mandarins of both the cultivars were negative and highly significant. Since weight loss was negatively, correlated with external characters, fruits which were either waxed or packed in containers lined with PE or cellophane films were given significantly more scores for appearance and firmness than those stored in boxes lined with either newspaper or waxpaper sheets. PE lining being the most effective treatment in the present studies to retard weight loss proved more effective for preserving the external characters than cellophane lining. However, waxing was comparable as this treatment gave an additional shine to the skin of mandarins. A problem encountered in case of FE lining was moisture condensation on the surface of mandarins which could encourage microbial growth and increase rot incidence. Earlier deterioration in external characters of late picked kinnows could be due to high temperature and low humidity of storage (23-36°0, 47.0-76.5 % RH).
Waxing with Fruitex (indigenous wax) resulted in off flavour development when Feutrell's Early and Kinnow mandarins were stored at ordinary room conditions. Hence, waxed fruits got less score in organoleptic evaluation tests as compared to control fruits. Dilution of Fruitex or use of commercial exotic waxes (Britex-561 and Seal Britex-56) and their diluted formulations could not solve this problem. No such problem of off-flavour development was encountered in fruits packed in boxes lined with different types of packaging material. Probable reasons for earlier onset of off-flavour development and lower flavour scores for control as well as treated lots in late harvestea kinnows was time of picking and high storage temperature (23-360C). Cellophane as a lining material in the present studies proved superior to waxing and other lining materials tested. It retarded weight loss and retained normal flavour of mandarins during storage at room conditions, hence preserved both the external as well as internal quality characters. Moreover, there was no problem of moisture condensation on fruit surface as happened in case of PE lining.
Maximum changes during 5 week storage (16-220C) of waxed and cellophane lined Feutrell's early mandarins occurred in ethanol contents which were followed by acetaldehyde, TSS/ acid ratio, TSS and acidity. Regression analysis revealed that correlation between TSS and flavour scores was non significant (r--O.373), relationship between TSS/acid ratios and flavour scores was linear and negative (y.--O.697), and that of total acids and flavour scores was linear but positive (r-O.740). There was a negative and highly significant linear relationship between ethanol contents and flavour scores (r--O.967) and acetaldehyde oontents and flavour scores (r--O.986). The coefficients of determination (r2) of flavour scores versus acetaldehyde, ethanol, total acids and TSS/acid ratio were 0.97, 0.94, 0.55 and 0.48, respectively. This indicates that above 90 variations in flavour scores can be explained by changes in ethanol and acetaldehyde contents whereas only about 50 % of variation in flavour scores can be predicted by changes in total acids and TSS/acid ratios. More changes in ethanol contents as compared to other internal chemical characters studied and its stronger correlation with flavour scores during storage of Feutrell's erarly mandarins prove its superiority as a chemical quality indicator during postharvest citrus fruit handling studies.
Comparatively more increase in ethanol and acetaldehyde, less increase in TSS and more decrease in total acids of waxed Feutrell's early mandarins could be due to anaerobic respiration during storage at room conditions. The ratio of ethanol and acetaldehyde (E/A) of waxed mandarins was also higher during storage than those of control or cellophane lined fruits. The E/A ratio gives an indication of oxidation-reduction state of coenzyme nicotinamide adenine dinucleotide (NAD) in plant tissues. During fruit maturation and senescence both E/A and NADH2/NAD have been reported to increase. Furthermore, a number of NAD-dependent oxidation reactions in orange juice vesicles have been reported to be depressed when the Redox ratio was increased. Similarly, flavour changes during storage in waxed mandarins with high E/A ratios in the present case might have been due to lowered activity of NAD-dependent oxidative reactions. The decrease in citric acid contents during storage of Feutrell's Early mandarins correlated to increase in E/A ratio at 1 % level of significance (r = O.75). Since the formation of oxaloacetic acid (the precursor of citric acid in Krebs cycle) requires the NAD-dependent oxidation of malic acid, this stronger linear relationship between these two variables indicates that citric acid metabolism is affected, and strengthens the hypothesis that NAD ratio is important in controlling metabolic pathways in citrus fruits.
Free amino acids identified in fresh kinnow juice in decreasing order of concentration were serine, aspartic acid, glutamic acid, arginine, threonine, proline, lysine, alanine, valine, cystine, glycine, phenylalanine, tyrosine, histidine, leucine, isoleucine and methionine. Preliminary investigations revealed that there was no effect of waxing on free amino acids of kinnows. However, there was a considerable decrease in most of the amino acids during postharvest storage at room conditions. Further studies are needed in this direction to understand the metabolism of free amino acids and their relation to internal quality deterioration during postharvest handling of citrus fruits.