Browsing by Author "Ambuko, J."

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A comparative evaluation of maturity indices of mango fruits produced in two contrasting agro-ecological zones of Kenya
(Ruforum, 2014) Ambuko, J.; Ouma, L.; Shibairo, Solomon I.; Hutchinson, M.; Njuguna, J.; Owino, WO.
Harvesting mango (Mangifera indica) fruits at the right stage for the destination market and use requires reliable maturity indices. There are various indices that are used to determine harvest maturity for mango fruits. However, differences in cultivars and growing environment affect the reliability of these indices. The present study was conducted to establish maturity indices of two popular mango varieties, ‘Apple’ and ‘Ngowe’. The study was conducted in two contrasting agro-ecological zones (AEZs) of Kenya namely Embu County (a high potential AEZ) and Makueni County (a low potential AEZ). For each variety, the earliest physiological maturity was determined using flesh color. The flesh color was established by cutting the fruits longitudinally to expose the cross sectional view. The earliest physiological maturity (stage 1) was marked as the stage when the flesh was mostly cream and turning yellow at the seed. The number of days after full bloom was matched to this maturity stage (stage 1) and subsequent maturity stages determined at 10-day intervals as stages 2, 3 and 4. For each of the maturity stages, physiological (ethylene evolution and respiration rates); physical (size, peel/flesh firmness and peel/flesh color) and biochemical (Total soluble solids - TSS, Total titratable acidity – TTA and TSS:TTA ratio) maturity indices were determined. The results show that in both varieties (‘Apple’ and ‘Ngowe’) from both locations (Embu and Makueni), respiration rates increased gradually with maturity. ‘Ngowe’ and Makueni fruits registered the higher respiration and ethylene evolution rates compared to ‘Apple’ and Embu fruits for the same maturity stage. As maturation progressed, peel firmness decreased gradually irrespective of variety or production location. In all fruits, flesh color (hue angle) decreased gradually with maturity. Total soluble solids increased while TTA decreased gradually with maturity. Overall, in both varieties, Makueni fruits attained comparable maturity indices to Embu fruits at an earlier stage/date. The results revealed the significant effect of production location on the maturity indices of mango fruits. There is need for additional studies to establish
Comparison of quality attributes of mango fruits produced from two contrasting agro-ecological zones of Kenya
(Ruforum, 2014) Ouma, L.; Ambuko, J.; Shibairo, Solomon I.; Owino, WO.; Hutchinson, M.; Njuguna, J.; Books, Ruforum.; Sheets, Fact.; Oer, Ruforum.; Scarda, Ruforum.
Mango (Mangifera indica) is a tropical fruit adapted to a wide range of agro-ecological conditions. In Kenya, mango fruits are produced across various agro-ecological zones (AEZs); from sub-humid to semi-arid. The diverse production conditions found in these AEZs variably affects fruit growth and subsequently the postharvest qualities. This study was conducted to compare the quality attributes of two mango varieties (‘Apple’ and ‘Ngowe’) produced under two different AEZs. Embu County (a high potential AEZ) and Makueni County (a low potential AEZ) are major mango-producing counties in Kenya. The study was conducted over two seasons between 2013 and 2014. ‘Apple’ and ‘Ngowe’ mango fruits were harvested from the two AEZs at four successive maturity stages; from the earliest physiological maturity (stage 1) to the tree-ripened stage (stage 4). In stage 1 fruits, the flesh was mostly cream and had just started turning yellow around the seed. The subsequent maturity stages were determined at 10-day intervals from stage 1 as stages 2, 3 and 4. For all the maturity stages, initial quality attributes were determined immediately after harvest and the again at a predetermined end stage following ripening at ambient room conditions (Temperature: 25 ± 1 oC and RH: 60 ± 5%). The quality attributes determined include sugars (fructose, glucose, and sucrose), °Brix, %TTA, vitamin C, beta carotene and mineral nutrients (Potassium, Magnesium, Calcium). For sensory evaluation, diced fruits were scored for various attributes including acidity, sweetness, mouth feel, flavor, aroma, color and general acceptability by a panel of 33 untrained panelists. For all the parameters evaluated, there was significant interaction (Pd”0.05) between maturity stage, variety and AEZ. Levels of TTA decreased gradually with the stage of maturity irrespective of variety and AEZ. Overall, Embu fruits had higher initial TTA levels for all maturity stages. Although Apple fruits (all stages) had higher initial TTA, at the end of ripening TTA levels were relatively lower compared to Ngowe. Initial beta carotene levels increased while vitamin C levels decreased with maturity stage. Significantly higher beta carotene and vitamin C levels (initial and end stage) were observed in Makueni fruits. Initial and end stage Ca, Mg and K levels decreased with maturity stage, irrespective of variety or AEZ. Stage 1 and 2 fruits retained the highest Ca and Mg levels at the end stage. The highest sugar levels and end stage 0brix levels were observed in stage 4 fruits (regardless of AEZ and variety). Overall, Makueni fruits had relatively higher end stage 0brix levels compared to Embu fruits. In ‘apple’, Makueni fruits scored higher than Embu fruits for all the sensory attributes. On the contrary in ‘Ngowe’,
Effect of accel (gibberellins (ga4+7) + benzyladenine) on the shelf life of French beans, phaseolus vulgaris L.
(2003) Ambuko, J.; Emong'or, E.V.; Shibairo, Solomon I.; Chemining'wa, G.N.
To determine the effects of Accel on the shelf life of French beans, Phaseolus vulgaris L. variety Monel, two field experiments were conducted at the University of Nairobi’s Kabete Field Station for two seasons. Accel was sprayed at 12.5, 25.0, 37.5 and 50.0 mg/litre to the bean plants to run off just before flowering. The field experiments were followed by laboratory experiments where the effect of Accel on water content and moisture loss by the French bean pods after storage was determined. Chlorophyll content of fresh pods at harvest and that retained by the pods after eight days of storage was also determined. Increase in Accel concentration led to a linear increase in the water content of pods. Accel reduced moisture loss by the pods thereby reducing the extend of wilting. A pplication of Accel significantly increased fresh pod chlorophyll content and enhanced chlorophyll retention in the pods after storage. The response to increasing Accel concentration was linear.
Effects of ethephon and potassium nitrate on off-season flower induction in mango
(2014) Maloba, S.; Ambuko, J.; Hutchinson, M.; Owino, W.O.
Mango (Mangifera indica) fruit production in Kenya is seasonal with peak and off seasons – one of the contributing factors to postharvest losses. Off-season flower induction is a strategy that can be used to address mango seasonality. Manipulation of mango trees to produce an off-season crop can be achieved through application of flower induction chemicals. In the present study, the two flower induction chemicals, potassium nitrate (KNO3 ) and ethephon were evaluated on two mango varieties: ‘Apple’ and ‘Ngowe’. The study was conducted in two agro-ecological zones (AEZs) of Kenya namely, Embu County (a high potential AEZ) and Makueni County (a low potential AEZ). The age of the trees used in the experiment were of similar size and vigor with an average age of 6 to 8 years. Potassium nitrate was applied at two concentrations (2 and 4%), while ethephon was applied at three concentrations (300, 600 and 1000ppm) and compared to a control (water). Prior to spraying, 100 terminal shoots were marked randomly on each tree for percentage flowering determination. After inflorescence development, 20 panicles per tree were marked randomly on each tree to monitor fruit set. The experiment was laid out in a randomized complete block design with three replicates and three trees per treatment. Effect of the treatments was established from reproductive growth parameters including days to flowering and fruit set, number of panicles per tree and average fruit set per 20 panicles. Potassium (4%) increased percentage flowering (% of tagged shoots) in both ‘Ngowe’ and ‘Apple’ in both AEZs. In Embu, 4% KNO3 resulted in 46% flowering in ‘Ngowe’ compared to 4% in ‘Apple’. On the contrary, in Makueni, the response was greater in ‘Apple’ (60%) compared to ‘Ngowe’ (27%). Response to ethephon increased with concentration with the 1000 ppm giving the best response; 22 and 28% flowering (% of tagged shoots) for Embu and Makueni, respectively, in ‘Ngowe’. In both AEZs and varieties, flowering was d” 3% in untreated controls. Time to flowering was significantly shortened by both KNO3 and ethephon treatments with ‘Ngowe’ being more responsive than ‘Apple’. Significant treatment effect (pd” 0.05) was observed on fruit set with 4% KNO3 and 1000 ppm ethephon resulting in the highest fruit set in both AEZs and varieties. The findings reveal the potential of KNO3 and ethephon to induce off-season flowering in ‘Apple’ and ‘Ngowe’. Further studies are on course to optimize the treatments for commercial application.
Efficacy of activebag® packaging on postharvest quality of purple passion fruit (passiflora edulis Sims)
(2014-08-17) Owino, W.O.; Yumbya, P.; Shibairo, Solomon I.; Ambuko, J.
Water loss after harvest results in wilting and shrivelling and is one of the major causes of postharvest losses in perishables. Passion fruit is susceptible to rapid water loss after harvest leading to diminished quality and limited longevity. This study evaluated the efficacy of Activebag®, a new modified atmosphere packaging product in the Kenyan market, to maintain quality and prolong the shelf life of purple passion fruit. Fruits were harvested at 60-65 and 75-80 days after anthesis with peel color being 50-70% and full purple respectively. Fruits were either packaged in Activebag® or ordinary polyethene bags and allowed to ripen under ambient room conditions. Evaluation of the physiological parameters included ethylene production rate, respiration rate, cumulative weight loss and other physicochemical parameters associated with ripening and quality. In both stages unpackaged fruits lost more weight compared to packaged fruits. The two forms of packaging (active bag and ordinary bag) effectively reduced weight loss though the difference between the two was not statistically significant (P>0.05). Both forms of packaging also significantly reduced and delayed the rate of respiration (both stages), ethylene production and other postharvest quality attributes. These results indicate that Activebag® packaging was most effective in fruits harvested at stage 60-65 days after anthesis as it maintained the quality and prolonged the shelf life by eight days longer compared to ordinary packaging.