​Partial Characterization of Custard Powder Prepared from Native and Modified Non-conventional Starches

Starch contributes greatly to the textural properties of many foods and is widely used in food and industrial applications as a thickener in milk-based sweets and jellies; soups; sauces; custards and dessert (Basim et al., 2004). Non-conventional sources such as sweet potato, jackfruit seeds, dioscorea are good source of starch and has been less utilized as compared to conventional sources. So, it is necessary to utilize these underutilized crops for their use in many foods and non-food applications (Sarkar, 2016; Sarkar and Jindal, 2015). Non-conventional starches and their value addition have increasingly been gaining importance in recent years because of their potential application as functional ingredients in the development of new products (Goni et al., 2008). Root and tuber crops are mostly consumed fresh or used as animal feed However, in recent years in many countries, there has been an increasing scientific awareness of the importance of increasing root crop production (Hahn et al., 1989).  Modification of starch improves their functional properties and  broaden their application.
      
Sweet potato (Ipomea batatas) is dicotyledonous plan from Convolvulaceae family an important crop in many developing countries and some parts of the world sweet potato is the staple crop (Radley, 1976; Collins and Walter, 1982). Sweet potato contains approximately 20% starch and  most of the sweet potatoes are consumed as simple food products (e.g. fresh, steamed, or roasted snacks) or used as an animal feed. Until now, starch is the main industrial product from sweet potatoes but its use is still limited (Jangchud et al., 2003). The jackfruit (Artocarpus heterophyllus) a highly seasonal fruit widely available in tropical countries of the world however due to its abundance in peak season it is underutilized (Akter et al., 2018). At present, India is the largest producer with a production of 1.4 million tons per annum (Sawe, 2017). The fruit can reach up to 36 kg in weight and it comprises of approximately 100 to 500 seeds which make up 8-15% of the whole fruit (Tran et al., 2016). The seeds are reported to be powerhouse of nutrients, containing approximately 14% protein, 80% carbohydrate and also contain an abundance of starch, approximately 60-70% of its dry weight (Chen et al., 2016). However, the seeds are often discarded as they are not usually consumed (Dutta et al., 2011). Yam belongs to family Dioscoreacea and is a monocotyledous tuber bearing plant, from the genus  Dioscorea  (Ayensu, 1972). Yam is mostly consumed locally  or retained for planting owing to poor shelf life of the tubers profound amount is lost during storage (Wheatley, 2000). Post harvest  utilization of tuber will improve earnings from this crop. The high starch content of the tuber have huge market potential for the exploitations.
      
As custard prepared from custard powder serves as a great boon to seriously ill patients as it is an instant energy source and also to patients having dysphagia (Barczi et al., 2000). Dysphagia  patients need thickened fluids which may be either pre-packaged ready-to-use or freshly- prepared from powder thickeners dissolved in water, cordial, fruit juices and milk. Corn starch is preferred for preparation of custard powder, however in India, corn has become the third important food grain after wheat and rice. The demand for corn is growing up in India with the setting up of food processing units involved in production of breakfast cereals and snacks. The alternative non conventional sources which are underutilized and available in abundance can be used in the production and modification of starch. Shaikh et al., 2017 reported custards were prepared using modified pearl millet had improved cold storage stability, pasting, textural and sensory properties overall quality of custard. Very few literatures are available on utilization of modifies starches from non- conventional sources in custard powder. So, the present study focuses on optimization of process parameters for the development of custard powder using modified starches and its quality evaluation.

Starch isolation and modification
 
Sweet potato starch was isolated as described by Singh et al., (2005). Starch from jackfruit seed cotyledons were isolated as per Mukprasirt and Sajjaanantakul (2004). Starch from dioscorea was extracted as per method described by Riley et al., (2006). To alter the properties of native starches two types of modifications - heat moisture treatment (Collado and Corke 1999) and hydroxypropylation crosslinking (Raina et al., 2006) were performed. Sweet potato, jackfruit seeds  and dioscorea were purchased from local market. All chemicals used for the study were of analytical grade. The work was carried during period of 2015-2-16 in College of Community Science, Central Agricultural University, (I), Meghalaya, India.
 
Preparation of custard powder
 
The custard powder was prepared as per the following formulation i.e. starch (98%), sunset yellow colour (1%), vanilla flavor (0.9%) and salt (0.1%).
 
Characteristics of custard powder
 
Moisture content of the custard powder prepared by sweet potato, diascora and jackfruit seed starches (native and modified) was measured by A.O.A.C., 2005. Bulk density and hygroscopicity was measured as per Goula et al., 2004; Cai and Corke 2000. The color of the starches was measured by a chroma meter (CR-300, MIN LTA, Japan) as L, a and b values.
      
Preparation of the model custard system was performed according to the recipe and protocol of COST Action 921 (Santonicoa et al., 2008).
 
Quality evaluation of custard
 
Viscosity was measured by digital brookfield viscometer; spindle no.6 at 100 rpm, at constant temperature (10-15°C) for 5 min. Soluble solids content of prepared custard was determined with a hand refractometer (Gonzalez et al.,2009).

Custard texture measurements were carried out with the TA.XT2i Texture Analyser (Stable Micro Systems Ltd, Surrey, UK) with a 5 kg load cell. Back extrusion cell (A/BE) with 35mm diameter compression disc was used.
      
Sensory evaluation was conducted on the custard samples after one-day storage at 4°C temperature.
 
Sensory characteristics
 
Appearance, color, aroma, texture (mouth-feel), taste, after-feel and overall acceptability were evaluated by semi trained panel members on 9-point hedonic scale.
 
Statistical analysis
 
Analysis of variance (ANOVA) with Tukey’s standardized range test was performed and samples were analyzed, at a significance level of p≤0.05.

Characteristics of custard powder
 
Moisture content and hygroscopicity
 
Moisture contents of all the custard powders was found to be higher than commercial custard powder (Table1).The bulk density was higher for custard powder prepared from hydroxypropylated crosslinked dioscorea starch was found to be lower for custard powder prepared from hydroxypropylated crosslinked jackfruit seed starch (Table 1).
 

      
Hygroscopicity of custard prepared from jackfruit seed  starch was found to be higher viz. 3.930% than the custard powders prepared from other native starches which could be attributed to the higher water binding capacity of jackfruit seed  starch (Table 1). The custard powder prepared from heat moisture treated starch samples showed higher bulk density than custard powders prepared from native starches which was due to hydrophilic tendency of heat moisture treated starch samples (Singh et al., 2009).  Custard powders prepared from hydroxypropylated crosslinked starch showed lower hygroscopicity than other custard powder prepared from native as well as heat moisture treated starch.
 
Color measurement
 
Color of custard powder prepared from sweet potato was observed to be higher than the color of other starches. Among all custard powder samples L value for the custard powder prepared from native sweet potato starch was higher viz. 98.808. While the b value was found to be higher for custard powder prepared from both hydroxypropylated crosslinked starches as well as heat moisture treated starches than the custard powder prepared from their native counterpart (Table 2).
 

 
Quality evaluation of custard
 
Viscosity measurement
 
The viscosity for custard prepared from hydroxypropylated crosslinked starch containing custard powder was found to be higher among all custard samples prepared from custard powder samples which were basically formulated with native as well as modified starches while viscosity was found to be lower in case custards prepared from custard powder samples containing heat moisture treated starch samples. Viscosity ranged between 950-3510cP for all the custard samples. Custard prepared from custard powder containing heat moisture treated starch samples was found to be lower viz. 950cP for dioscorea starch and (Table 3). The viscosities of custard prepared from custard powder containing native as well as hydroxypropylated crosslinked starches was found to be higher than the custard prepared using commercial custard powder.
 

 
Soluble solid content
 
Soluble solid content for all custard samples was found to be in the range of 28-29°bx which was well comparable with the commercial custard sample.
 
Texture analysis
 
Texture is a criterion by which quality is judged and an important factor when selecting or rejecting products (Rosenthal, 1999). Firmness, consistency and adhesiveness of the custard was measured using texture analyzer (Table 4). Custard prepared from all the custard powder samples had good textural properties viz. custard powder prepared from native starches produced good firmness, consistency as well as adhesiveness well comparable with the commercial custard sample. The firmness of the custard prepared from custard powder containing hydroxypropylated crosslinked sweet potato starch was found to be higher (0.715N) among all the custard samples which is much higher than commercial custard samples. Firmness was found to be lower in case of custard prepared from custard powder containing heat moisture treated starch samples when compared to their native counterparts.

      
Custard prepared from custard powder containing hydroxypropylated crosslinked sweet potato starch showed highest consistency (8.055Ns) while custard prepared from the custard powder containing heat moisture treated starch samples showed lowest consistency.
 
Sensory evaluation
 
Sensory evaluation plays an important role in measuring characteristics and acceptability of food products. The sensory profile data of the custard samples prepared from different custard powder are shown in Table 5.
 

 
Appearance
 
The custard prepared from custard powder containing hydroxypropylated crosslinked starch was higher next to commercial custard samples.
 
Color
 
The evaluation scores obtained for coded samples showed that color of custard prepared from commercial custard was more appealing than other custard samples.
 
Mouthfeel
 
Mouthfeel of all the custard samples was described and scored in terms of thickness, melting and creaminess by the panelists. Custard prepared from custard powder containing hydroxypropylated crosslinked sweet potato starch obtained score of 8.18 which was higher than the commercial custard sample obtained score of 8. The panelists commented that hydroxypropylated crosslinked sweet potato starch sample showed higher thickness, meltiness and creaminess when taken in mouth.
 
Taste
 
Taste of all the custard samples was acceptable by the panelists. The score obtained by commercial custard sample was 8.18. The lowest score obtained by custard prepared from jackfruit seed starches.
 
After-feel
 
Custard prepared from custard powder containing native starches as well as heat moisture treated starches showed lower after-feel than that of commercial custard as well as hydroxypropylated crosslinked starch samples.
 
Overall acceptability
 
Overall acceptability of custard prepared from hydroxypropylated starch samples was higher than custard prepared from custard powder containing native and heat moisture treated starches. Custard prepared from custard powder containing hydroxypropylated crosslinked sweet potato starch was more acceptable next to commercial custard sample.

Non conventional starches could be better utilized for potential application as functional ingredients in the development of new products and they will be better alternative to conventional sources. Custard prepared from custard powder containing hydroxypropylated crosslinked starches showed higher firmness, consistency and adhesiveness than custards prepared from custard powder containing heat moisture treated starches. Thus it can be concluded that good quality custard can be prepared from non conventional sources and which can be used as a dessert, filling or sauce, added to cakes, puddings, pastries, or filled with fruit and served as fruit custard. The prepared custard will be a boon to elderly people, ill patients and for patients with dysphagia.

Research was funded by Ministry of Food Processing Industries, New Delhi