Nutrient composition and shelf life evaluation of instant soup mix from dehydrated vegetables

Introduction

What role can processed vegetable products play in bridging the nutritional gap that affects millions of consumers who rely on ready-to-eat meals? Convenience foods have become a significant part of daily diets across both urban and rural populations, driven by time constraints and shifting lifestyle patterns [1] . Among these, instant soup mixes represent one of the fastest-growing segments in the packaged food market, valued for their ease of preparation and long storage potential [2] . Yet many commercially available soup mixes are loaded with synthetic flavouring agents, excess sodium, and artificial preservatives, raising concerns about their long-term health effects [3] . Dehydrated vegetables offer a practical alternative to fresh produce, especially in regions where seasonal availability and cold-chain infrastructure remain limited [4] . The dehydration process removes moisture to levels below 10%, which slows microbial growth and enzymatic degradation while preserving a large proportion of the original vitamins and minerals [5] . Carrots, spinach, tomatoes, and onions are widely consumed and rich in betacarotene, iron, lycopene, and quercetin respectively [6] . But the drying conditionstemperature, air velocity, and slice thickness affect the final nutrient retention and colour of the product [7] . Several researchers have attempted to develop soup mixes using dried legumes, mushrooms, and cereal blends [8,9] . However, fewer efforts have focused on formulations that rely primarily on mixed vegetable powders with minimal additives. Shelf life data for such products under different storage regimes also remain sparse in the published literature [10] . The present research aimed to develop three instant soup mix formulations from dehydrated vegetables, evaluate their proximate composition, assess their sensory attributes, and monitor their microbial stability over a 90-day storage period at two different temperatures.

Methods

Preparation of dehydrated vegetable powders: Each vegetable was washed, sorted, and sliced into uniform pieces (3-4 mm thickness). Blanching was performed in hot water at 95°C for 2 minutes to inactivate polyphenol oxidase, followed by immediate cooling in ice water. The blanched slices were spread on stainless steel trays and dried in a cabinet dryer at 60°C with an air velocity of 1.5 m/s for 8 hours until the moisture content dropped below 8%. Dried slices were ground using a hammer mill and sieved through a 60-mesh screen [11] . Three formulations were prepared by blending vegetable powders and spice mixes at different ratios: Formulation A (40:30:20:10 carrot: spinach: tomato: onion with 5% spice), Formulation B (30:30:25:15 with 7% spice), and Formulation C (35:25:25:15 with 4% spice).

Proximate and shelf life analysis: Proximate composition (moisture, protein, fat, crude fibre, ash, and carbohydrate by difference) was determined following AOAC [12] standard procedures. Each analysis was performed in triplicate. For shelf life evaluation, 50 g portions of each formulation were sealed in aluminium-laminated pouches and stored at ambient temperature (28±2°C) and under refrigeration (4±1°C). Samples were withdrawn at 0, 15, 30, 60, and 90 days for microbial analysis (total plate count and yeast and mould count) using standard pour plate technique [13] .

Sensory evaluation was conducted on day 0 by a trained panel of 15 members using a 9-point hedonic scale assessing colour, aroma, taste, texture, and overall acceptability.

Quality control

All analytical equipment was calibrated before each batch of measurements. The moisture analyser (Model HE53, Mettler Toledo) was verified against a certified reference material with known moisture content of 10.0±0.2%. Triplicate measurements were taken for every parameter, and results were accepted only when the coefficient of variation fell below 5%. Culture media for microbial testing were autoclaved at 121°C for 15 minutes and checked for sterility by incubating blank plates alongside inoculated samples. Temperature loggers were placed inside both storage units and recorded readings every 6 hours throughout the 90-day period.

Results

The three soup mix formulations differed noticeably in their proximate profiles and sensory scores. Microbial counts stayed within safe limits under refrigeration for the entire monitoring period, while ambient-stored samples showed a gradual rise in colony-forming units after the second month. Formulation B contained the highest protein and fibre values among the three variants, which can be attributed to its greater proportion of spinach powder (30%) and higher spice blend content. Formulation C showed the lowest moisture and highest carbohydrate values, reflecting a comparatively higher share of carrot and onion powders in its blend.

Comprehensive interpretation

Taken as a whole, the results point to Formulation B as the most promising candidate for further development. Its superior protein and fibre content, combined with the highest sensory scores, make it a strong option for healthoriented consumers. The shelf-life data confirm that aluminium-laminated packaging under refrigerated conditions can keep the product safe for at least 90 days, though ambient storage beyond 60 days should be approached with caution given the rising microbial load observed in all formulations.

Discussion

The protein content of Formulation B (9.1 g/100 g) was higher than the 6.3 g/100 g reported by Chen and Liu [8] for a mushroom-oat soup blend. This difference likely stems from the relatively high protein concentration in dried spinach leaves, which can contain up to 29 g protein per 100 g on a dry-weight basis [14] . For consumers seeking plantbased protein alternatives, even modest increases in the protein density of convenience foods carry practical significance. Dietary fibre values in the current formulations (5.4-7.9 g/100 g) compare favourably with earlier work on legumecereal soup mixes, where fibre ranged from 4.1 to 6.8 g/100 g [9] . The blanching step may have contributed to fibre retention by softening cell walls without extensive leaching, as suggested by Li et al. [5] . And because fibre supports satiety and digestive health, its preservation during drying is a meaningful quality indicator [15] . Regarding shelf life, the total plate count at day 90 under ambient storage approached but did not exceed the 4.0 log CFU/g limit set by Chinese national standards for dried food products [16] . Refrigerated samples stayed well below 2.0 log CFU/g. These patterns align with findings from Wang and Zhao [10] , who observed similar microbial trends in dehydrated herb mixes stored at comparable temperatures. The low water activity of the products (below 0.6) was the main factor restricting microbial proliferation, though the oxygen barrier properties of the laminated pouches also played a protective role.

Conclusion

This research set out to develop instant soup mixes from dehydrated carrots, spinach, tomatoes, and onions, and to assess their nutritional quality and storage stability. Formulation B, which used a 30:30:25:15 vegetable ratio with 7% spice blend, emerged as the best variant on the basis of both proximate composition and sensory acceptability. It recorded the highest protein (9.1 g/100 g) and crude fibre (7.9 g/100 g) among the three formulations. Sensory panel scores were significantly higher for Formulation B in four of the five assessed attributes. Microbial counts for all formulations remained within acceptable limits for 90 days under refrigerated storage, though ambient-stored samples showed counts nearing the upper safety boundary by day 90. These results suggest that dehydrated vegetable soup mixes can serve as a practical, nutrient-retaining convenience food product, particularly in settings where access to fresh vegetables is seasonal or limited. Future work should explore the inclusion of proteinInternational Journal of Agriculture and Food Science https://www.agriculturaljournals.com rich ingredients like chickpea or lentil flour to further improve the amino acid profile, and accelerated shelf life testing would help predict product behaviour over longer storage periods.

Acknowledgement

AcknowledgementsFunding sources: This research was supported by an internal grant from the Hainan Island College of Tropical Agriculture for applied food technology research. Institutional support: The authors thank the Food Processing Laboratory of the college for providing equipment and facilities used throughout the experimental work. Contributions: The authors acknowledge the assistance of laboratory technicians who helped with microbial plating and sensory panel coordination.

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