Study on shelf life of hot air puffed barnyard millet

Introduction

Millets are nutrient-dense and hold a significant role in the diets of individuals in various areas across the globe. Despite their nutritional advantages over cereals, millets are primarily consumed by traditional users and those from lower-income groups (Jaybhaye et al. 2014) [9] . Barnyard millet is the most ancient cultivated small millet. The primary species of Barnyard millet are Echinochloa esculenta, known as Japanese Barnyard millet or Japanese millet, and Echinochloa frumentacea, referred to as Indian Barnyard millet. The barnyard millet from India is referred to as Billion Dollar Grass (USDA NRCS. 2002) [24] . Echinochloa frumentacea belongs to the Poaceae family and is a self-pollinating plant. Echinochloa frumentacea is the toughest millet and is widely recognized by various names such as Sanwa and Jhangora (Hindi), Shyama (Sanskrit), Oodalu (Kannada), Kuthiravaali (Tamil), Udalu and Kodisama (Telugu), Shamul (Marathi), Sama (Gujarati), Shamula (Bengali), and Swank (Punjabi). It is grown in several nations, including India, China, Japan, Malaysia, the East Indies, Africa, and the United States (Anuradaha et al. 2014) [1] . In India, it is predominantly grown in Orissa, Maharashtra, Madhya Pradesh, Tamil Nadu, Bihar, Punjab, Gujarat, and the hills of Uttarakhand (Kumar et al. 2000) [12] . Barnyard millet is an excellent grain. Though comparable to rice and wheat, it also contains minerals and vitamins, making it an interesting source of valuable nutrients such as carbohydrates, fats, proteins, and dietary fiber. Due to their slow digestibility rate, barnyard millets serve as a good protein source with low carbohydrate levels, positioning them as a natural nutraceutical food, particularly beneficial for those at high risk of non-infectious diseases like diabetes, heart conditions, obesity, and cancer (Rajeswari and Priyadharshini, 2021) [19] . Millets provide distinct health benefits as they are rich in micronutrients, especially minerals and B vitamins, as well as nutraceuticals. While millets aren't a major component of the daily diets in America and Europe, these regions have now acknowledged their significance as an ingredient in gluten-free and multigrain cereal products. Nonetheless, in several Asian and African nations, millet serves as the primary food for the inhabitants of millet-producing regions and is utilized to create a variety of traditional dishes and drinks such as idli, dosa, papad, chakli, porridges, breads, baby foods, and snacks (Chandrasekara et al. 2011) [3] . Nowadays, numerous RTE (ready-to-eat) snacks, including fried chips, wafers, flakes, granules, extruded and spiced items, popcorn, and puffed cereals, have become essential elements of consumer eating patterns. Popping or the preparation of expanded items from cereals and legumes is a traditional food processing technique utilized to create RTE light and crispy products (Ushakumari et al. 2007) [25] . Puffing grains is a traditional method of preparing grains for snacks or breakfast cereals, served either plain or with added flavours, salt, or sugar. Starch is the primary element in human diet and provides a variety of essential functional characteristics. The quality of starch is evidently dependent on its structure and preparation (Lehman et al. 2007) [14] . Puffed grain, as a pre-cooked Ready-to-eat ingredient, can serve in snack foods, specialty items, and as a foundation for creating supplementary foods (Hoke et al. 2005) [8] .

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In accelerated shelf-life testing (ASLT), products are stored in a precisely controlled setting that aims to speed up the deterioration process of the product. To develop models predicting shelf life in different storage conditions, the deterioration rate can be compared to that under standard ambient conditions. While accelerated tests yield valuable outcomes, numerous risks arise if the tests are conducted improperly. Sullivan et al. (1974) [22] , performed storage studies to assess the stability of explosion-puffed, dried potato cubes concerning the emergence of browning and undesirable flavours. The findings from this storage test indicate that all samples kept at 23 °C or below, irrespective of the packaging atmosphere, maintain stability in browning and flavour over the course of one year. Another type of degradation of breakfast cereals postprocessing and packaging is moisture absorption, leading to a loss of the unique crispy texture. The appropriate type and quality of moisture vapour-proof packaging materials prevents moisture absorption (Fast, 1987) [6] . The reduction in crispiness of hot-air puffed kodo millet was notably less in MMPE, followed by PP, HDPE, and LDPE packages (Farzana et al. 2022) [5] . Quast and Karel, (1972) [18] documented critical water activity for popcorn and potato chips as 0.50 and 0.40, respectively. Khodke, (2002) [11] indicated a crucial water activity of 0.48 for dehydrated ready-to-eat potato cubes. Nath, (2006) [15] indicated that the critical water activity values for RTE potato and RTE potato-soy snack foods were approximately 0.471 and 0.449, respectively. The water activity of the product was viewed as a measure of the shelf life of crispy items, as noted by previous researchers (Labuza and Medellin 1981; Katz and Labuza, 1981; Tubert and Iglesius, 1986) [13,10,23] .

Materials and Methods

Storage of hot air puffed grain samples

Storage investigations of hot air puffed Barnyard Millet were carried out at 40 °C and 95% relative humidity, focusing on packaging materials for the final puffed grain products made under optimized processing conditions. Metalized Polyester (MP) and HDPE were utilized for storage experiments (Pawar, 2018) [17] .

Sorption isotherm of hot air puffed grain samples

The sorption isotherm behaviour of the puffed grain sample under environmental conditions was analyzed to show the impact of water activity (a W ) on moisture content. The Texture Analyser was used to assess crispness, the main factor for product approval concerning differences in moisture level. These studies determined the essential moisture level and crucial water activity at which the product became less crisp (Pardeshi, 2008) [16] .

Determination of water vapor transmission rate (WVTR) of packaging material

A ten-gram dried silica gel desiccant was placed in a small glass beaker without a spout, and the packaging materials selected for the experiment effectively covered the beaker's opening. A saturated solution of potassium nitrate (KNO 3 ) was utilized in the desiccator to keep the temperature at 40±1 °C and relative humidity at 90±1% for every beaker. The beakers holding the silica gel desiccant were weighed consistently every 24 hours for ten days. The overall moisture absorbed by silica gel was assessed in beakers wrapped with MP and HDPE packing materials (Sahu and Khokhar, 2024) [20] .

The permeability of packaging material was calculated using following equation:

Where, W = weight gain by desiccant (g) θ = time (days) The values of permeability for given thickness of the packaging materials was determined as per given by Khodke, (2002) [11] and Pardeshi, (2008) [16] .

Shelf life calculation

The time required for the moisture content of the puffed grain sample to increase from an initial value of Mi (kg water per kg dm) to its critical value Mc, at which it lost its crispness, was computed numerically to establish the shelf life of the puffed product "θ" (days). (Balaji, 2020) [2] (Das, 2005) [4] . ) ... (Geankoplis, 1983) [7] …. (2.3) K A = permeability of the packaging material (kg m-2 day-1 Pa-1) A' = area of the package (m2) RH = relative humidity in which package is placed (fraction) a W = water activity (fraction) of the product at T °C = f (M) a Wc = critical water activity and is less than or equal to RH M = Moisture content of the puffed product (kg water per kg dm)

i and c = are the suffix for initial and critical moisture contents respectively.

Result and Discussion

Storage Studies of the Hot Air Puffed Barnyard Millet Grain

This segment explores the changes observed in the hot airpuffed grains stored at 40 °C with 95% relative humidity. As noted earlier in Section 2.1, the puffed grains were maintained in identical conditions within two types of packaging materials (MP and HDPE). Pawar, (2018) [17] utilized this packaging material for a storage study of readyto-eat snacks made from sprouted soy fortified millet flour

Properties of Packaging Materials

As indicated in section 2.3, measurements tracked the total moisture increase over time by silica gel contained in two pouches, namely Metalized Polyester (MP) and High Density Poly Ethylene (HDPE), at 40±2 °C and 95±1% relative humidity. The WVTR was determined using the slope of the relevant curves, and the findings are presented in Table 1.

Sorption isotherm of the hot air puffed grains

Sorption isotherms of puffed grains at 40±1°C and 95% RH, showing the variation of moisture content (MC, kg/kg dm) of the puffed grains with water activity (a W ) are given in Fig. 1. The critical water activity (a Wc ) value of the hot air puffed barnyard millet with 0.0968 kg/kg dm critical moisture (MCc) content was found to be 0.63. Moisture content increased slowly with increase in water activity.

Moisture content of hot air puffed millets during storage:

The variation in the product's moisture content under various storage settings is shown for hot air-puffed Barnyard Millet and depicted in Fig.

2 The moisture level rise from 0.0477 kg/kg dm to 0.1080 kg/kg dm in the HDPE pouch and from 0.0477 kg/kg dm to 0.0821 kg/kg dm in the MP pouch over the 0 to 28 days of the accelerated storage period. According to Fig. 2, puffed barnyard millet stored in MP pouch is practically displayed a shelf life 52 days, while the HDPE pouch showed 21 days, both kept at 40 °C and 95% RH under accelerated storage conditions. The estimated shelf life was determined using Eq. 2.2, as shown in [26] . A small reduction in the crispness of breakfast cereal was observed at a W < 0.5. Subsequently, a swift decline in crispness was noted until a W = 0.8, at which point the product entirely lost its brittleness (Sauvageot and Blond, 1991) [21] . The critical moisture content (MCc) and critical water activity (a Wc ), at which the produce lost its crispness, were identified by Pardeshi (2008) [16] . Research by Balaji (2020) [2] indicates that as water activity rises, moisture content swiftly escalates after reaching a critical moisture threshold. The fluctuation in moisture levels for puff millet was greater than that in HM-HDPE packs and lesser in MFF packs

Storage Studies of Hot Air Puffed Barnyard Millet Grain

In each case, it was found that the moisture level rise rapidly as time passed. The moisture content varied more when the puffed millets were packed in high-density polyethylene (HDPE) than when they were packed in metalized polyester (MP). The level of moisture in food items is essential for influencing their shelf life. Moisture levels usually increase or decrease during storage, based on the storage conditions and type of packaging. The longer shelf life in MP relative to HDPE may be due to the fact that MP pouches possess better barrier properties than HDPE. Comparable findings by Pawar (2018) [17] examined sprouted soy-fortified composite flour-based RTE snack foods and noted that at extremely high humidity (95%), the snack foods' shelf life diminished to 24 days in HDPE and 40 days in MP

Conclusion

References

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