Maize (Zea mays) is one of the most important cereal grains in the world. It is third behind rice and wheat (Mbuya et al., 2011) and serves as a staple food for approximately 400 million people in developing countries. It is used in these countries as food, ingredient and animal  feed   (Odebode  et  al.,  2008). About half  of  the estimated 603 million tonnes world production of maize is produced in developing countries (Samapundo et al., 2007). Various types of maize exist and include pop, dent, flint, floury and sweet cultivars (Bibiana et al., 2014). Maize (Zea mays saccharata), also known as sweet corn, or  green  maize  differ from all other types of maize, because it contains the gene sugary1 (su1), which contributes to its high sugar content (Marshall, 1987) and retains large amount of sugar in the kernels, hence it is named ‘sweet’. According to Robinson and Treharne (1985), a recessive gene on the fourth chromosome is what slows down the conversion of some of the sugar into starch.

Maize is known always to be sweet when freshly harvested and readily loses its sweetness in less than three days if not properly handled (Robinson and Treharne, 1985). The degradation observed in maize sweetness during storage is attributed to the high respiration rate after harvest; hence this work investigated postharvest treatments that can reduce the loss of sugar and moisture contents so as to retain freshness. The conventional method of storing/ preserving fresh maize include canning, film packaging and freezing methods which is associated with some limitations such as high cost of packaging materials, transportation and high electric energy requirements thus, there is a need for low cost but effective technology like steeping.

Packaging of freshly harvested maize in plastic films stored at ambient tropical conditions (temperature of 28-30°C and relative humidity of 70-80%) have been reported to significantly reduce moisture loss and maintained the appearance and kernel firmness of maize (Oluwalana et al., 2017). However, the method was found not to show any significant effect in sugar content retention and extension of storage life of fresh maize at ambient temperature (Bello and Oluwalana, 2017). Combination of plastic film packaging and storage at low temperatures of 5-10°C have been reported by Bello and Badejo (2017) to significantly preserve the sweetness and other nutritional composition for 8 days.

This study explored the steeping method as an alternative to film packaging and cold storage. Steeping in food, involves immersion of food substance into solutions which have preservative potentials. Natural substances such as salt, sugar, vinegar and diatomaceous earth are used as traditional preservatives. Salt is considered antibacterial since it restricts bacterial growth by lowering the amount of free water molecules in foods as bacteria need high moisture to survive and thrive. Sugar also acts as preservative and maintain desirable appearance, flavour, colour and body in products (Ravneet et al., 2009). Hence the aim of this work was to investigate the effect of steeping in salt, sugar and salt-sugar solutions on the proximate composition and sugar retention of fresh sweet maize.

Freshly harvested maize was purchased from the Teaching and Research Farm of The Federal University of Technology, Akure and was immediately taken to the Department of Food Science and Technology, The Federal University of Technology, Akure where the studies were carried out.

Sample preparation

The husk and silk of the freshly harvested maize were removed, shelled and well mixed before being portioned 1 kg each into 5 L jars. Two (2) litres of steeping solutions of salt, sugar, salt-sugar was added to the maize in separate jars and each sample were replicated. The jars were then closed with air-tight lids. The control was kept at room temperature without any form of preservation. All the containers (jars) which were 12 altogether were kept in ambient conditions (28 ± 2°C and 70% RH).

Sampling method

Samples for each treatment were taken as described by AOAC (2005) and analyses were carried out at intervals of 7 days and 3 days for proximate composition and sugar content determinations respectively. The treatments were 8% salt solution (SAFM), 10% sugar solution (SUFM), 2:3 v/v salt-sugar solutions (SSFM) and the control with no solution (control).

Chemical analysis

Samples of the maize were analysed for moisture, ash, fat, crude fibre, protein and carbohydrate contents according to the methods described by AOAC (2005). Protein content was determined by the Kjeldahl-Nitrogen analysis procedure, using 6.25 as a conversion factor whiles the crude fat was determined using the Soxhlet extractor. The carbohydrate content was obtained by difference. Sugar content was determined using phenol sulphuric acid method as described by Masuko et al. (2005).

The use of salt-sugar solution in this study was found to be more effective in keeping the qualities of freshly harvested maize as it had better retention of the proximate composition and sugar content than the other solutions. However, sugar solution alone showed a better potency for preservation than the salt solution alone. Thus, the salt-sugar solution can be recommended for fresh maize short term storage for sweetness retention.

The authors have not declared any conflict of interests.