Assessment of drying methods on nutritional quality of dried fruits in small-scale processing facilities

Thesis Abstract

Drying is a critical preservation step for fruits in small-scale processing facilities, yet the specific drying methods employed may differentially impact the retention of essential nutrients, bioactive compounds, and sensory quality, with direct implications for product safety, shelf-life, and market competitiveness. This study addresses the problem of inconsistent nutritional outcomes in dried fruits produced by small-scale operators due to variability in drying technologies and process parameters. The aim is to evaluate how conventional (sun-drying, shade-drying), mechanical (hot-air, freeze-drying, vacuum-drying), and hybrid (solar-assisted hot-air) drying methods affect the nutritional quality, including macronutrient retention, vitamin C, total phenolics, flavonoids, carotenoids, mineral content, hydration properties, and microbial safety, in relation to process conditions. Specific objectives are (i) to quantify nutrient retention across drying methods for common fruits (maple juice apricot, peeled mango, and tree tomato) sourced from five small-scale processing facilities; (ii) to assess system-level factors—energy use, processing time, and capital/operational costs—associated with each method; (iii) to model relationships between drying parameters (temperature, humidity, thickness, and unit energy consumption) and nutritional outcomes using multivariate regression; (iv) to evaluate sensory acceptability and consumer-perceived quality of dried fruit products; and (v) to develop evidence-based guidelines for selecting drying methods under varying facility constraints. The study adopts an embedded mixed-methods design, combining quantitative experimental evaluation with qualitative insights from facility operators. The population comprises small-scale fruit processing facilities in a defined peri-urban district, with a purposive sample of 12 facilities providing access to three fruit types over one harvest season. A split-sample approach uses (a) laboratory-controlled drying trials at a central facility to standardize comparisons (n=180 dried fruit samples per fruit–method combination, replicated thrice) and (b) on-site observational data and product sampling (n=360 samples) from participating facilities. Quantitative data include proximate composition (protein, fat, carbohydrate), vitamin C by high-performance liquid chromatography (HPLC), total phenolics and flavonoids by spectrophotometric assays, carotenoids by HPLC, mineral analysis by ICP-OES, water activity, moisture content, colorimetry, texture profile analysis, and microbial load (total viable count, molds and yeasts). Energy consumption and drying kinetics are recorded in situ. Qualitative data are collected through semi-structured interviews with facility operators and descriptive process logs, analyzed through thematic analysis to identify practical constraints and decision-making criteria. Validity and reliability are ensured via standardized analytical protocols, calibration checks, inter-laboratory validation for proxy measurements, and triangulation across data sources. Data analysis employs ANOVA and multivariate regression to compare nutritional outcomes across methods, with post hoc tests to identify significant differences; principal component analysis (PCA) elucidates patterns among nutrients; regression models quantify the influence of drying parameters on nutrient retention; and thematic analysis interprets operator perspectives. Expected findings include superior retention of heat-sensitive micronutrients (vitamin C, phenolics) with controlled-temperature mechanical methods (vacuum-drying, freeze-drying) at optimized moisture targets, while sun and shade drying demonstrate greater losses but lower energy demands; hybrid drying shows intermediate performance with favorable energy efficiency. The study anticipates a trade-off between energy, processing time, and nutritional quality, with contextual differences by fruit type and facility capability. The contribution to knowledge lies in providing empirically grounded, scalable evidence on how drying method choice shapes nutritional outcomes in small-scale fruit processing, informing policy and extension services, and offering practical decision-support tools for operators. The main conclusion is that method selection should align with targeted nutrient retention goals, available energy infrastructure, and market requirements; the study recommends adopting hybrid or mechanical drying with precise control of temperature and moisture, complemented by routine nutrient monitoring and cost-benefit analyses to optimize product quality and economic viability. Policy recommendations include provision of affordable energy-efficient dryers, training on drying parameter optimization, and guidance on product labeling to reflect nutrient quality differences.