Bagging prevents russeting and decreases postharvest water loss of mango fruit cv. ‘Apple’

In Kenya, the mango (Mangifera indica L) cultivar ‘Apple’ is commercially important but it often suffers excessive russeting, which both compromises its appearance and impairs its postharvest performance. Together, these effects seriously reduce its market potential. Exposure to surface moisture is implicated in russeting of cv. ‘Apple’ mango. The objective was to establish the effect of bagging on russeting. Developing fruit were bagged at the onset of the exponential growth phase, using brown paper bags (Blue star®). Un-bagged fruit served as controls. The brown paper bags were selected because of their high permeance to water vapor. At harvest maturity, bagged fruit were larger, less russeted and had smaller lenticels than un-bagged control fruit. Staining with aqueous acridine orange in conjunction with fluorescence microscopy revealed numerous microcracks and larger lenticels on un-bagged control fruit but these were not evident on bagged fruit. Postharvest mass loss (principally water loss) of bagged fruit was lower than of un-bagged control fruit. In the un-bagged control fruit, the skin's water permeance increased as the russeted surface area increased (r2 = 0.88 **). Fruit skins were less permeable to water vapor than the brown paper bags. The brown paper bags contributed not more than 4.2 to 9.1% of the total in-series diffusion resistance of skin + bag. The masses of isolated cuticular membranes, and of dewaxed cuticular membranes, and of wax per unit surface area were higher for un-bagged control fruit than for bagged fruit. Bagged fruit were also greener and showed less blush. There was little difference in skin carotenoid content between bagged and un-bagged control fruit, but skin anthocyanin content was lower in bagged fruit. The rates of respiration and ethylene evolution of bagged fruit were lower than those of un-bagged control fruit. There were no differences between bagged and un-bagged control fruit in their organoleptic and nutritional properties including titratable acidity, total soluble sugars, sucrose, glucose, fructose, vitamin C and calcium content. In conclusion, bagging decreased russeting and increased postharvest performance of fruit of mango cv. ‘Apple’

Surface Moisture Induces Microcracks and Increases Water Vapor Permeance of Fruit Skins of Mango cv. Apple

Exposure to surface moisture triggers cuticular microcracking of the fruit skin. In mango fruit cv. apple, microcracking compromises postharvest performance by increasing moisture loss and infections with pathogens. This study reports the effects of exposing the fruit’s skin to surface moisture on the incidence of microcracking and on water vapor permeance. Microcracking was quantified microscopically following infiltration with a fluorescent tracer. Water mass loss was determined gravimetrically. Moisture exposure increased cuticular microcracking and permeance. During moisture exposure, permeance increased over the first 4 d, remained constant up to approximately 8 d, then decreased for longer exposure times. Fruit development followed a sigmoid growth pattern. The growth rate peaked approximately 103 days after full bloom. This coincided with the peak in moisture-induced microcracking. There were no increases in water vapor permeance or in microcracking in control fruit that remained dry. When experimental moisture exposure was terminated, microcracking and water vapor permeance decreased. This suggests a repair process restoring the barrier properties of the fruit skin. Histological analyses reveal a periderm forms in the hypodermis beneath a microcrack. Our study demonstrates that surface moisture induces microcracking in mango cv. apple that increases the skin’s water vapor permeance and induces russeting

Lenticels are sites of initiation of microcracking and russeting in ‘Apple’ mango

The mango cultivar ‘Apple’ is an important fruitcrop in Kenya, but it is highly susceptible to russeting. The objective was to establish whether lenticels predispose cv. ‘Apple’ mango to russeting. Fruit mass and surface area increased in a sigmoidal pattern with time. The frequency of lenticels per unit surface area decreased during development. The number of lenticels per fruit was constant. Lenticels were most frequent in the apex region and least common in the cheek and nak (ventral) regions. The cheek region also had lenticels with the largest core areas, whereas the lenticel core areas in the apex region were significantly smaller. Microscopy revealed stomata became covered over with wax deposits at 33 days after full bloom (DAFB). By 78 DAFB, periderm had formed beneath the pore. At 110 and 161 DAFB, cracks had developed and the periderm had extended tangentially and radially. The presence of lenticels increased the strain released upon excision of an epidermal segment, further strain releases occurred subsequently upon isolation of the cuticle and on extraction of the cuticular waxes. The number of lenticels per unit surface area was negatively correlated with the fruit surface area (r2 = 0.62 **), but not affected by fruit size. Mango cv. ‘Apple’ had fewer, larger lenticels and more russet, compared with ‘Ngowe’, ‘Kitovu’ or ‘Tommy Atkins’ mango. In cv. ‘Apple’, the lowest lenticel frequency, the largest lenticels and the most russeting occurred at a growing site at the highest altitude, with the highest rainfall and the lowest temperature. Moisture exposure of the fruit surface resulted in enlarged lenticels and more microcracking of the cuticle. Our results establish that russeting in ‘Apple’ mango is initiated at lenticels and is exacerbated if lenticels are exposed to moisture

Can calcium sprays alleviate jelly seed in mango fruits?

Jelly seed is a major challenge in mango production leading to enormous losses in the value chain. This internal fruit disorder is characterised by disintegration of cells, consistency of jelly and broken cells. Calcium plays an important role in enhancing tissue stability and firmness thus reducing cell disintegration. A two-year field study was conducted in Embu County, Kenya using ‘Van Dyke’ cultivar trees of approximately 10 years old. The objective of the study was to investigate the effect of varied sources of calcium, applied at different rates and timing on jelly seed occurrence and tissue calcium distribution. Calcium  in the form of calcium chloride, calcium nitrate and  easygro®  were applied at 1.0%, 1.5%, 2.0% or 0% (control) at three stages of  fruit development  (fruit set, 30 days after fruit set and 30 days to anticipated physiological maturity). The experiment was set up in a randomised complete block design with a split-split arrangement replicated three times. Fruits were harvested at physiological maturity and ripened at ambient conditions (28±1̊C, 75-80 RH). Data collected included: jelly seed occurrence, calcium distribution (exocarp, mesocarp, endocarp and cotyledon) and fruit weight. Jelly seed occurrence and calcium distribution were determined at ripe stage. All the calcium sources invariably suppressed the occurrence of jelly seed. Calcium chloride (2.0%) applied at fruit set had the lowest average jelly seed score of 1.2 and 2 in seasons I and II respectively. There was a significant negative relationship between fruit weight (r = -0.55, r = -0.52), calcium content in the exocarp (r = -0.56, -0.49), mesocarp (r = -0.52,-0.76), endocarp (r= -0.76, -0.66) and jelly seed incidence occurrence. This suggested that calcium has a role in alleviating jelly seed disorder. Application of calcium at fruit set was more effective in suppressing jelly seed occurrence than later applications. Calcium chloride (2.0%) applied at fruit set was more effective in reducing jelly seed occurrence. There is need to study further on soil based calciumand other calcium formulations on the effects on jelly seed occurrence

Evaluating the Potential of Juice from Some Sweet Sorghum Varieties Grown In Kenya to Crystallize

Sweet sorghum (Sorghum bicolor (L) Moench) is a crop analogous to sugarcane with similar accumulation of sugars in its juicy stems. An earlier research study on agronomic trials carried out by Jomo Kenyatta University of Agriculture and Technology established that some of the imported varieties of Sweet Sorghum had sufficiently high amounts of sugar content in their Juice. The present study was undertaken with the objective of determining the potential of some of these sweet sorghum varieties to produce crystal sugar. This was with the long term goal of trying to find alternative uses for sweet sorghum. The sweet sorghum varieties were planted at the University research farm, and stalks of sixteen varieties were crushed using electrical roller mill to produce SS juice which was then subjected to a number of analyses including, total and specific sugar determination and apparent purity. The total sugars in degree Brix varied from 15.050 to 21.500, sucrose concentration ranged from 6.05g/l to72.77g/l, glucose 2.65g/l to 16.41g/l and fructose 2.66g/l to 17.16g/l whereas apparent purity(AP) ranged from 33.89% to 83.91%.The variation could have been  brought about by varietal differences. The juice of variety RIO had the highest sucrose purity of 83.91% which was further clarified by liming and double carbonation method. The resulting juice was concentrated into syrup by evaporation. Supersaturation for crystallization was attained by cooling, followed by seeding. According to the present study, the following sweet sorghum cultivars; Rio, CMSXS636, IESV91018LT, IESV93042SH and SPV1411 could have potential in crystal raw sugar production because they have AP greater than 75% and a relatively higher sucrose concentration. The Rio sweet sorghum variety with the highest sucrose purity of 83.91% and sucrose concentration of 40.86g/l was selected and subjected to crystal sugar production processes. The Rio juice subjected to crystallization process failed to produce crystals probably due to the presence of dextran, aconitic acid and starch. Key words: Brix, Sucrose, apparent purity, Clarification, Crystal Sugar,

Effects of grain source and processing methods on the nutritional profile and digestibility of grain amaranth

Amaranth grain is reputed to have a high nutritional value, and as a plant, be tolerant to adverse weather conditions. This suggests that grain amaranth could be useful in tackling malnutrition and the growing burden of cardiometabolic diseases. However, there is insufficient knowledge at present about how the nutrient composition and digestibility of amaranth grain varies with growing environment, crop genotype, and post-harvest processing. We investigated the effect of the source and processing of amaranth grains on the digestibility of protein and lipid present in the grains. There was variation in the composition and digestibility of raw grains from different sources, indicating a role of genotype and/or growing environment which warrants further investigation. The greatest differences in digestibility were measured between the different processing techniques. This indicates that efforts to increase the cultivation and consumption of grain amaranth need to be supported by education about effective processing and preparation techniques

On-farm maize storage systems and rodent postharvest losses in six maize growing agro-ecological zones of Kenya

Rodents are one of the major postharvest pests that affect food security by impacting on both food availability and safety. However, knowledge of the impact of rodents in on-farm maize storage systems in Kenya is limited. A survey was conducted in 2014 to assess magnitudes of postharvest losses in on-farm maize storage systems in Kenya, and the contribution of rodents to the losses. A total of 630 farmers spread across six maize growing agro-ecological zones (AEZs) were interviewed. Insects, rodents and moulds were the main storage problems reported by farmers. Storage losses were highest in the moist transitional and moist mid-altitude zones, and lowest in the dry-transitional zone. Overall, rodents represented the second most important cause of storage losses after insects, and were ranked as the main storage problem in the lowland tropical zone, while insects were the main storage problem in the other AEZs. Where maize was stored on cobs, total farmer perceived (farmer estimation) storage weight losses were 11.1 ± 0.7 %, with rodents causing up to 43 % of these losses. Contrastingly, where maize was stored as shelled grain, the losses were 15.5 ± 0.6 % with rodents accounting for up to 30 %. Regression analysis showed that rodents contributed significantly to total storage losses (p < 0.0001), and identified rodent trapping as the main storage practice that significantly (p = 0.001) lowered the losses. Together with insecticides, rodent traps were found to significantly decrease total losses. Improved awareness and application of these practices could mitigate losses in on farm-stored maize

Mango Fruit Processing: Options for Small-Scale Processors in Developing Countries

Postharvest losses of mango fruit in a number of developing countries in Africa and Asia have been estimated to be as high as over 50%, especially during the main harvest season. Micro, small, and medium scale food processing enterprises play an important economic role in developing economies in processing of a diversity of healthy food products as a sustainable way to reduce postharvest losses and food waste, extend shelf life of food, boost food security, and contribute to national gross domestic product. Processing of mango fruit into the diverse shelf-stable products makes the seasonal fruit conveniently available to consumers all year round. Over the years, research and food product development have contributed substantially to a number of unique and diverse processed mango products with specific qualities and nutritional attributes that are in demand by a wide array of consumers. These mango products are derived from appropriate food processing and value-addition technologies that transform fresh mango into shelf-stable products with ideal organoleptic, nutritional, and other quality attributes. Some of the common processed products from mango fruit include pulp (puree), juice concentrate, ready-to-drink juice, nectar, wine, jams, jellies, pickles, smoothies, chutney, canned slices, chips, leathers, and powder. Minimum processing of mango fruit as fresh-cut product has also gained importance among health-conscious consumers. Apart from the primary products from mango fruit, mango pulp or powder can be used to enrich or flavor secondary products such as yoghurt, ice cream, beverages, and soft drinks. Byproducts of mango processing, such as the peel and kernel, have been shown to be rich in bioactive compounds including carotenoids, polyphenols, and dietary fibers. These byproducts of mango processing can be used in food fortification and manufacture of animal feeds, thereby gaining greater value from the fruit while reducing wastage. This review focuses on the current trends in processing and value addition of mango applicable to small-scale processors in developing countries

Effects of pretreatment during drying on the antioxidant properties and color of selected tomato varieties

Drying is essential in lowering the water activity and increasing the shelf stability of perishables. Thus, this study investigated the effect of pretreatment on the retention of the antioxidant properties and color of four tomato varieties; that is, Anna F1, Kilele, Prostar F1, and Riogrande during drying. Prepared quarters were treated by spraying with 0.5% sodium metabisulfate, 0.5% calcium chloride, and distilled water. The quarters were oven dried at 50°C, 60°C, and 70°C to 13% moisture content. Lycopene, β carotene, total phenolics, color, and moisture content were determined in both the fresh and dried samples. Initial moisture content among the four varieties did not differ significantly and ranged between 94.2 and 94.6%. Results showed that the main effects were significant (p &lt; .05) on all measurable variables. Significantly (p &lt; .05) higher retention levels in lycopene, β carotene, total phenolics, and lightness was observed in chemically pretreated samples compared to the control during drying