Production, Utilization and Processing of Kenyan Guavas: Development of Nutrient-enriched Guava Nectars From Local Varieties

Abstract

In Kenya, guava (Psidium guajava L.) is a neglected nutrient-dense fruit that grows from randomly dispersed seeds. Despite being highly nutritious, the industrial processing of the fruits is non-existent in the country, with limited traditional and household processing. The goal of this study was to document the current trends in the production, postharvest handling, utilization, processing, and marketing of locally produced guava fruits, as well as to evaluate standardized processing techniques of the local varieties into nutrient-rich nectars. A mixed-methods study design employing qualitative and quantitative approaches was adopted whereby desk reviews followed by a cross-sectional baseline survey on the status quo of the guava value chain Taita Taveta and Kitui Counties of Kenya (n=417) were conducted. Experimental study designs involving completely randomized designs, factorial designs, and comparative analysis were used to evaluate the physicochemical and processing qualities of Kenyan guava varieties, effects of pulping methods on the physicochemical properties of guava pulp, differences in the physicochemical properties of commercially traded nectars, and the effects of blending guava nectars with moringa leaf extract on their acceptability, nutritional profile, and shelf stability. The results indicate that the crop is highly neglected with limited postharvest handling and preservation, leading to high losses among approximately 77 % of households interviewed. Although the country's annual production exceeds 11 Metric tons, estimated to be worth $ 1.1 million, most yearly produce (84 %) is from sprouts of wild seeds, with red- and white-fleshed varieties growing in 97% and 49 % of the households, respectively. Minimal incomes were realized annually ($ 0.5-400) among homes that sell fresh fruits (30%) due to low farm gate prices of $ 0.08 – 0.10. Guava processing was limited, and only 3% of households reportedly processed guavas due to a lack of value addition techniques (75%) and appropriate processing equipment (66%). xxv The physicochemical characterization of the guavas indicated significantly (p=0.008) wide intra- and inter-fruit variations among the red-fleshed, white-fleshed, and strawberry guavas. Physically, the fruits' length, diameter, and weight varied with the average pulp to seed ratio significantly (p=0.026) higher in the red guava than in the white and strawberry guavas, at 31.2, 17.8, and 12.1, respectively. The strawberry guava levels of vitamin C were low and averaged 164.11±11.85mg100-1g dry weight (d.w) compared to the white guava's 1665.56±126.50 mg100-1g d.w. The white-fleshed guavas were limiting (p=0.0001) in β-carotenes (0.04±0.06 mg100-1g d.w) in comparison to the strawberry guava’s (1.55±0.30 mg100-1g d.w). The red-fleshed guava had significantly (p=0.014) high levels of total phenolics (1649.14±329.70 mgGAE per 100-1g d.w) and antioxidant activities (1989.14± 383.47 μMTE 100-1g d.w). The red-fleshed guava significantly (p<0.05) outperformed the white in all key aspects -micronutrients and phytochemical composition (except for vitamin C) and would therefore be the most ideal for processing given its resilience and adaptation across various agro-ecological zones. The effect of pulping methods on the quality of white- and red-fleshed guavas showed that although hot extraction methods resulted in significantly (p=0.001) high yield (67 -77%) as compared to the cold (62 – 72 %), there were no significant (p=0.0619) differences in the moisture loss during pasteurization, averaging 2.59±5.41 –5.1±2.6%. However, the vitamin C losses were significant (p=0.001), with up to 60% and 64% of the white and red guavas lost respectively. The cold extraction method resulted in significantly (p<0.05) better retention of the vitamin β-carotene (1.9±0.4mg), zinc (5.6±2.1mg), iron (20.1±8.6mg), calcium (19.2±4.2 mg), flavonoids (241.3±56 mgCE), phenolics (1548.7±25.8 mg GAE) and antioxidant activities (1998.6±333μMTE) per 100g. xxvi The consumers clearly distinguished formulated guava nectars based on a minimum of 25% of red-fleshed guava pulp and blended nectars with 12.5 - 20% Moringa oleifera leaf juice extract inclusion. The formulations' mouthfeel had the highest discriminating power (test power 3.94, p=0.0004), differentiating the nectars. Inclusion of moringa leaf extract up to 12.5% resulted in fairly similar overall acceptability as the unblended nectars at 5.9±0.8 and 5.3±0.9, respectively. The moringa leaf extract significantly (p<0.05) resulted in high zinc (4.62±2.14 mg100-1g), iron (28.87±6.21mg100-1g), potassium (87.4±5.3mg100-1g), vitamin C (574.2±116.2 mg100-1g), β-carotene (0.34±0.03 mg100-1g), flavonoids (217.0±18.8 mgCE100-1g), phenolics (1934.8±198.3mgGAE100-1g), and antioxidant activity (1934.8±198.3 μMTE 100-1g) compared to the unblended nectars. The most acceptable nectars would be shelf-stable for at least five months regardless of the packaging type, blending, or length of storage with significant (p=0.000) changes in the TSS, pH, and the TTA. The yeast and molds (<10cfu/g) and the TVCs (<10 cfu/ml) did not surpass the maximum allowable limits of 30 and 100 cfu/ml, respectively. However, considerable (p<0.0001) color deterioration was observed, notably in nectars packaged in transparent packaging. Despite variations in Kenyan guava varieties, the fruits are nutrient-dense, with high annual losses due to limited processing and thus a lack of guava products made from the local fruits. However, this study demonstrated that adopting processing techniques for the red-fleshed guava, which have superior nutritional and processing qualities, at the household and small-scale levels would result in nutrient-enriched guava nectars, which could aid in strengthening the guava value chains by improving guava farmers' livelihoods and consumer access to processed fruits when they are out of season.