Browsing by Author "Njuguna, 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
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    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’,