Effect of Microwave Treatment on the Shelf-Life Characteristics of Date Burfi during Storage

Introduction

Traditional Indian dairy products occupy a unique position in the country's food culture, combining nutritional value with sensory appeal and social significance. An estimated 50-55% of milk produced in India is converted into a wide array of traditional sweets and delicacies, many of which are prepared using traditional techniques involving coagulation, desiccation and fermentation (Balasubramanian, 2024) [1] . Among these, Burfi stands out as one of the most popular Khoa-based confections, widely consumed during festivals, celebrations and as a gift item symbolizing joy and goodwill. Burfi is valued not only for its distinctive body, texture and flavour but also for its high content of milk solids, including fat, protein, lactose and minerals, which contribute significantly to its nutritional profile (Yadav et al., 2024; Hs and Kg, 2022) [1,3] . In recent decades, consumers increasingly seek foods that offer both indulgence and functional benefits, prompting researchers and industry to explore novel formulations that integrate traditional dairy bases with nutrient-dense ingredients. Such innovations not only enhance the nutritional quality of conventional sweets but also align with contemporary consumer preferences for natural, functional and culturally familiar foods (Ortiz et al., 2017) 41] . Date (Phoenix dactylifera L.), often referred to as the "tree of life," has been a staple food in arid regions for thousands of years due to its exceptional nutritional composition and energy density. Dates are rich in carbohydrates (44-88%), contain moderate amounts of protein (2.3-5.6%), minimal fat (0.2-0.5%), and are an excellent source of dietary fibre (6.4-11.5%), essential minerals such as potassium, calcium, magnesium, iron and phosphorus, and B-complex vitamins (Saeed et al., 2024; Mahomoodally et al., 2023) [5,6] . Beyond their macronutrient profile, dates exhibit antioxidant, antimutagenic and antimicrobial properties, and their regular consumption has been associated with potential benefits in managing conditions such as anemia, bone disorders, cardiovascular diseases and oxidative stress (Sedighi-Khavidak et al., 2022) [7] .

The incorporation of date paste into dairy products thus offers a practical strategy to enhance their nutritional and functional attributes while imparting a distinctive flavour and natural sweetness. Traditional milk-based sweets like Burfi are highly perishable because of their high moisture, nutrient-rich composition and susceptibility to microbial and chemical spoilage. During storage, microbial growth, moisture migration, lipid oxidation and non-enzymatic browning reactions collectively reduce shelf life and impair sensory quality (Vijayalakshmi et al., 2005) [8] . Conventional preservation strategies such as chemical preservatives, vacuum packaging and refrigeration can extend shelf life but often increase costs, modify product characteristics or encounter consumer resistance due to concerns about synthetic additives. This has stimulated interest in affordable, efficient and consumer-acceptable technologies that improve microbial safety and storage stability without compromising sensory and nutritional attributes (Ranathunga et al., 2023) [9] . Microwave technology offers a promising non-conventional thermal processing alternative for dairy sweets. Microwaves (commonly 2,450 MHz) generate heat volumetrically through dipolar rotation and ionic conduction, enabling rapid, energy-efficient processing with better retention of heat-sensitive nutrients and improved product quality compared with conventional surface heating (Meshram et al., 2017; Kakar et al., 2024) [10,11] . Studies on concentrated dairy sweets indicate that microwave post-packaging treatment slows microbial proliferation, reduces moisture loss and delays sensory deterioration, extending shelf life by several days under ambient conditions and substantially longer under refrigeration (Sabikhi et al., 2018) [12] . Given the nutritional benefits of date-enriched Burfi and the proven potential of microwaves in similar products, systematic evaluation of microwave power-time combinations on the physicochemical, sensory and microbiological quality of date Burfi during storage is warranted. Such research would advance understanding of microwave-food interactions in dairy-fruit matrices and provide practical guidance for producers seeking cost-effective preservation technologies. Accordingly, the present study was undertaken with the following objectives: (i) to standardize microwave powertime combinations for date Burfi; (ii) to evaluate the influence of microwave treatment on the physicochemical attributes, including moisture, HMF, FFA and titratable acidity; (iii) to assess the sensory quality of microwavetreated date Burfi during storage at ambient (30 ± 1 °C) and refrigerated (10 ± 1 °C) conditions; (iv) to determine the effect of microwave processing on microbial load, specifically standard plate count and yeast and mould count; and (v) to establish the shelf life of microwave-treated date Burfi in comparison with untreated controls. The findings of this research are expected to provide a scientific basis for the adoption of microwave technology as a viable postpackaging intervention to enhance the quality and shelf stability of date-enriched traditional dairy sweets.

Materials and Methods

Materials: Good quality seedless dates ("Falcon" brand) and pooled buffalo milk were procured from the local market of Pusad city. All chemicals used for analysis were of analytical reagent grade. Key reagents included copper sulphate, potassium sulphate, boric acid, sodium hydroxide, sulfuric acid, iso-amyl alcohol, phenolphthalein indicator, hydrochloric acid, nitric acid, acetic acid, buffer tablets (pH 4 and 7), mixed indicator, phosphotungstic acid, Thio barbituric acid, potassium iodide, mercuric chloride (Himedia Laboratories, Mumbai), ammonia solution, oxalic acid, zinc sulphate, diethyl ether, petroleum ether, ethyl alcohol and trichloroacetic acid (AR Grade, Molychem, Mumbai).

Equipment's

The following equipment were used: digestion and distillation assembly for protein estimation (KELPLUS, Pelican Instruments, Chennai); research polarimeter 220 MM (BD Instrumentations, Ambala); UV-Vi's spectrophotometer (Electronics India, Mumbai); DTC-96 muffle furnace (Innovative Muffle Furnace, Mumbai); and a domestic microwave oven (2450 MHz, variable power settings 180-900 W).

Preparation of date Burfi

Date Burfi was prepared following the method of Vyawahare et al. (2022) [13] . Buffalo milk was concentrated by heat desiccation to prepare Khoa. Date paste was prepared by crushing soft seedless dates. Burfi was prepared by blending Khoa, sugar (@ 30% of Khoa) and date paste (@ 30% on Khoa basis, as optimized in preliminary trials) with uniform mixing. The mixture was kneaded at 60°C, set, cut into uniform pieces and packed.

Standardization of microwave treatment

Date Burfi samples (approximately 100 g each) were packed in low-density polyethylene (LDPE) pouches previously sanitized with 0.5% hydrogen peroxide solution. The packaged samples were subjected to microwave treatment at different power-time combinations to identify acceptable treatments without charring or excessive fat separation. The selected treatments were: M1 (180 W for 100 s), M2 (360 W for 50 s), M3 (540 W for 40 s), M4 (720 W for 30 s) and M5 (900 W for 20 s). Untreated samples served as control (TC).

Storage study

Microwave-treated and control samples were stored at two temperatures: ambient (30 ± 1°C) and refrigerated (10 ± 1°C). Samples were analyzed on days 1, 3 and 7 (30 ± 1°C) and days 1, 7, 14 and 21 (10 ± 1°C) for sensory and microbiological parameters.

Physicochemical analysis

Moisture, total solids, protein, fat, ash, lactose, titratable acidity and pH were determined as per IS: SP (Part XI) and AOAC methods. Hydroxymethylfurfural (HMF) content was estimated by the method of Keeney and Bassette, and free fatty acid (FFA) content was determined as % oleic acid.

Sensory evaluation

A panel of seven trained judges from the College of Dairy Technology evaluated samples for colour, appearance, body and texture, flavour and overall acceptability using a 9-point hedonic scale. Samples were served at room temperature (~30°C) in coded, closed HDPE containers.

Microbiological analysis

Standard plate count (SPC) and yeast and mould (Y & M) count were determined using appropriate media and incubation conditions. Results were expressed as colony forming units (CFU) per gram.

Statistical analysis

Data from three replications were subjected to one-way analysis of variance (ANOVA) followed by least significant difference (LSD) test at 5% level of significance using standard statistical methods (Snedecor and Cochran, 1989) [14] .

Results and Discussion

Effect of microwave treatment on sensory quality Sensory scores for microwave treated date Burfi samples along with non-microwave treated control samples were given by trained panel of 7 judges from the institute. Score was given on 9-point hedonic scale. Study was carried out on both storage temperatures viz., 30±1℃ and 10±1℃ separately for each parameter.

Sensory quality of microwave treated Burfi during storage at 30±1℃ Color

It was observed from Table 1 that scores for color on day 1 was found to be significant. The highest score was recorded for M3 (7.88) and lowest for M2 (7.38) against control (7.72). Score for color on day 3rd was found to be nonsignificant. The highest score was recorded for M3 = M5 (7.50) and lowest for M1 (7.22) against control (7.33) on third day of storage. The scores recorded for color on 7th day of storage was also found to be non-significant. The color score observed for samples was high for M3 (6.69) and low for M1 (6.38) against control (6.50). It is observed that color score decreases gradually in all the treatments during storage period.

Appearance

It was observed from Table 1 that scores for appearance on day 1 was found to be non-significant. The highest score was recorded for M3 (7.72) and lowest for M2 (7.44) against control (7.88). Score for appearance on day 3rd was found to be non-significant. The highest score was recorded for M3 = M5 (7.50) and lowest for M1 (6.94) against control (7.22) on third day of storage at 30±1℃. The scores assigned for appearance on 7th day of storage was also found to be non-significant. The score for appearance observed for samples was high for M3 (6.50) and low for M1 (5.83) against control (5.72). It was observed from tabulated data that scores for appearance decreases gradually from first to last day of storage in all the treatments at 30±1℃ .This might be due to the loss in freshness of samples stored at 30±1℃. Sensory scores of microwave-treated date Burfi during storage at 30 ± 1°C are presented in Table 1.

Body and texture

It can be observed from Table 1 that scores for body and texture on day 1 was found to be non-significant. The highest score was recorded for M3 (7.77) and lowest for M1 (7.50) against control (7.88). Scores for body and texture on day 3rd was also found to be non-significant. The highest score was recorded for M3 (7.38) and lowest for M1 (7.00) against control (7.22) on third day of storage at 30±1℃. The scores recorded for body and texture on 7th day of storage at 30±1℃ was also found to be non-significant. The score for body and texture observed for samples stored at 30±1℃ was high for M3 (6.13) and low for M5 (5.83) which resembles control (5.83). It was observed from tabulated data that scores for body and texture decreases gradually during storage at 30±1℃. The decreased scores for body and texture during storage might be due to increase in hardness of samples due to moisture loss caused by microwave treatment.

Flavor

It was observed from Table 1 that scores for flavor was significant (p<0.05) on 1st day. The highest score was recorded for M5 (8.33) and lowest for M2 (7.55) against control (7.77). Score assigned for flavor was found to be significant on 3rd day while non-significant on 7th day. The highest score was recorded for M4 = M5 (7.69) and lowest for M1 (7.05) against control (7.11) on third day of storage at 30±1℃. The score given on 7th day for flavor of samples stored at 30±1℃ was high for M3 (6.44) and low for M1 (5.77) against control (5.72). It can be observed from data that scores for flavor decreases gradually in all the treatments during storage period at 30±1℃.

Overall acceptability

It can be observed from Table 1 that the overall acceptability score varied significantly (p<0.05) on 1st and 7th day while that on 3rd day was found to be nonsignificant. The scores assigned for overall acceptability on day 1 was in the order of M1<M2<M3<M4<M5. The highest score was recorded for M5 (8.05) while lowest for M1 (7.38) as compared to control (7.83). The score given on 3rd day was in the order of M1<M2<M5<M4<M3. The highest score was recorded for M3 (7.47), whereas lowest for M1 (6.94) against control (6.27). The score for overall acceptability on 7th day was decreased in the order of M1 (5.41) <M2 (6.02) <M4 (6.30) <M5 (6.50) <M3 (6.55). The highest score for overall acceptability was assigned for M3 (6.55), whereas lowest for M2 (5.94) against control (4.94). It can be observed from data that overall acceptability score decreases gradually in all the treatments during storage period at 30±1℃. Similar results were observed for Burfi by Solanki et al. (2002) and Naresh et al. (2009) [15,16] for Peda. They also observed the decrease in sensory scores with increase in level of microwave treatment and storage period of Burfi and Peda, respectively.

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