Influence of heat treatment on the nutrient composition and physicochemical characteristics of Adlai (Coix Lachryma-Jobi L.) and Obatanpa cross Lagkitan (OxL) corn variety (Zea Mays L. ‘Los Baños Lagkitan’)

*Magpantay, Jr., R.L., Barrion, A.S.A., Dizon, E.I. and Hurtada, W.A. Department of Nutrition and Dietetics, College of Science, Polytechnic University of the Philippines, Sta. Mesa, Manila 1016 Institute of Human Nutrition and Food, College of Human Ecology, University of the Philippines Los Baños, College, Laguna 4031 Institute of Food Science and Technology, College of Agriculture, University of the Philippines Los Baños, College, Laguna 4031


Introduction
Coix lacryma-jobi L. also known as Adlai belongs to the family Poaceae or the grasses, the same family to which wheat, corn, and rice belong. It is considered as one of the native crops consumed as food in the Philippines. Also, adlai is cultivated as a cereal in some parts of Asia. As a food source, adlai is as versatile as rice. It can be cooked and processed as the main ingredient for delicacies. The grain can be ground into flour and used to make bread, pasta, and porridge (Domingo, 2016). In Taiwan, adlai is prepared as a milk substitute (Coludo and Janairo, 2015). The pounded kernel is also made into a sweet dish by frying and coating with sugar. It can also be husked and eaten as it is just like peanuts. In the Philippines, adlai is being promoted by the government because of its high protein content and it contains calcium, phosphorus, iron, thiamine, riboflavin and niacin. It is also easy to plant and needs fewer requirements, like irrigation, than that of rice. Furthermore, it can be harvested in a short span of time.
Corn (Zea mays L.), on the other hand, have different varieties including what are locally called obatanpa corn and lagkitan corn. Obatanpa which is a Quality Protein Maize (QPM), is a nutritious and potential health food which contains B-vitamins, phenolic compounds, and essential amino acid (lysine and tryptophan) (de Guzman 2008 Heat treatment can lead to improvements in, or damage to, the nutritional composition of foods (Chukwu et al., 2010;Oghbaei and Prakash, 2016). Raw cereals are generally inedible and require cooking. One of the most common ways of consuming cereals is boiling in water. Boiling decreases the amount of nutrients but it can increase digestibility and bioavailability (Chukwu et al., 2010). Canning typically involves the heating of lowacid foods such as cereals at 121°C, with the goal of eliminating all mesophilic microorganisms, as well as spores of Clostridium botulinum, leaving the product 'commercially sterile' (Murano, 2014). In Japan and USA, cereals are steamed, sealed and sterilized, and then served to military (Juliano, 1993). The use of retortable pouches is economical (Varalakshmi et al., 2014) and may result in a fresher-tasting food (Cox et al., 2006) and nutrient retention (Rizvi and Acton, 1982) compared to tin cans.
The study aimed to determine the effects of boiling and canning on the proximate composition, caloric value, carbohydrate profile and physicochemical characteristics of Adlai, OxL corn and adlai-corn blend.

Raw materials
Tapol variety of Adlai was obtained from Southern Tagalog Integrated Research Center, Marawoy, Lipa, Batangas City, Philippines while OxL corn grits were obtained from the Institute of Plant Breeding, University of the Philippines Los Banos, Laguna, Philippines. Retortable pouches (ITDI-DOST, Philippines) of size 18 cm x 10 cm having a 4 layer configuration of 12 µm polyethylene terephthalate, 9 µm aluminum, 15 µm oriented polyamide, 70 µm polypropylene and the total thickness of 106 µm which can withstand the retort condition of 121°C were used as the packaging material.

Selection of adlai and corn blend
Preliminary study was conducted to determine the most acceptable adlai:OxL corn blend. Eleven combinations of adlai:OxL corn (100:0, 90:10, 80:20,70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90 and 0:100) were subjected to sensory evaluation using a 9-point hedonic scale. The procedure cited by Mabesa (1986) in setting up a sensory evaluation was followed. About 5 grams or one teaspoon of cooked adlai:OxL blend was served warm in a small plastic cup containers. Samples were coded using three digit numbers and the order of presentation to panelists was randomized. Also, distilled water was provided to the evaluators to cleanse the pallet. Results showed that 90% adlai:10% OxL corn was the most acceptable combination in terms of aroma, flavor, texture and over-all acceptability.

Sample preparation and canning treatment
The sample preparation and canning treatment were done at the Department of Science and Technology -Industrial Technology Development Institute (DOST-ITDI), Philippines. Samples were washed using distilled water to remove dirt and then cooked with chicken stock (170 ml stock/100 g sample) in an electric rice cooker. When cooked, to avoid any possible sources of contamination, 150 g of the samples were filled in retortable pouch then sealed using a band sealer with hot and cold compressor. After sealing, samples were placed in a horizontal autoclave machine and sterilized to 121 o C at 15 psi for 15 mins. The commercial sterility test was conducted to guarantee the microbiological control of canned food, as described by Zamora (2013). Cooked Meat Medium (CMM) and Tryptone broth (TB) was used to identify any anaerobic microorganisms' activities after sterilization process. After the incubation period of 5 days, the test tubes were examined. The obtained qualitative results were based on a visual evaluation of the turbidity of the medium and gas formation. Afterwards, gram staining was performed.

Determination of nutritional value and physicochemical properties
Raw, boiled and canned samples of the adlai. OxL corn and adlai-corn blend were tested. Water absorption and solubility gel consistency and gelatinization were measured as described in Testing Manual for Rice (Rice Technical Working Group, 1997). Samples were analyzed, in triplicates, for the proximate composition (moisture content, crude fat, crude protein, total ash, and nitrogen-free extract) following the procedure prescribed in AOAC (Horwitz and Latimer, 2005). Starch content was determined using the anthrone method while the amylose content was determined using a colorimetric assay by Williams et al. (1958).

Statistical analysis
All gathered data were analyzed using One-way Analysis of Variance (ANOVA) and Tukey's studentized range test at 5% significance level, if applicable.

Physicochemical properties
The physical appearance of cereals contributes substantially to its quality. Table 1 shows that all samples exhibited soft gel consistency (61-100 mm). Gel consistency measures the tendency of the cooked cereals to harden after cooling (Asghar et al., 2012). All samples displayed a high gelatinization temperature. This means that samples can be cooked above 74 o C and grains will exhibit relatively the same behavior during cooking. Water absorption index (WAI) is a measure of the quantity of water absorbed during cooking of cereals. Results showed that adlai and the adlai-corn blend exhibited a higher WAI (%) value than OxL corn (p<0.05) which is an indication of high amylose content of adlai (Asghar et al., 2012;Li et al., 2020). Moreover, adlai may expand more and may result to an increase in volume after boiling. On the other hand, there was no significant difference in all samples when it comes to water solubility index (WSI).

Nutritional value of adlai and OxL corn
Heat treatment may affect the nutritional quality of food. Effects of boiling and canning on the proximate composition and caloric value are given in Table 2. The moisture content of adlai, OxL corn and adlai-corn blend was significantly (p<0.05) increased after boiling and canning, ranging from 3.00% to 77.24%. The observed increase in moisture in the boiled and canned samples could be attributed to the absorption of cooking water into the endosperm that resulted in swelling and gelatinization of the starch (Christian and Vaclavik, 2010). These results agree with the reported increase in moisture content upon cooking in corn by 42% (Bradbury and Holloway, 1988) and in adlai (Manning et al., 2017). However, research had shown that low moisture content of food is desirable since it will reduce the activity of microorganisms (Kordylas, 1990). Although, canning process is designed to destroy the most heat-resistant microorganism, specifically the spores of Clostridium botulinum, which can produce a deadly toxin if they sprout and grow under the anaerobic conditions of canned food (MacDonald and Reitmeier, 2017).
The fat content of all the raw samples significantly (p<0.05) increased after boiling and canning. However, values for boiled and canned samples were not significantly (p>0.05) different. In contrary to a study of Budge and Parrish (1999), lipolytic enzymes will be deactivated with heat treatment which resulted in a decrease in the fat content of the food. One of the reasons for the increase in fat content is may be due to the chicken stock that was used in cooking the samples. However, the nutritional content of the chicken stock was not established.
The protein content ranges from 7.42% to 11.94%. Boiling significantly (p<0.05) decreased the protein content of Adlai, OxL corn and adlai-corn blend by 2.9%, 11.45% and 7.22%, respectively and by 1.2%, 12% and 7.5%, respectively, after canning (p<0.05). The decrease in protein is due to the denaturation wherein the hydrogen bonds and the non-polar hydrophobic interactions in proteins are disrupted by heat (Olajide et al., 2011). This observation agreed with findings that proteins in corn were degraded and become more soluble when heated (Chukwu et al., 2010). It was also reported that protein of powdered adlai decreased significantly upon heating (Manning et al., 2017).
Fiber content of processed adlai, OxL corn and adlaicorn blend samples varied significantly between 0.13%, 1.96% and 0.16% for boiling, and 0.08%, 1.87% and 0.07% for canning. The fiber content of canned samples was significantly lower than that of raw and boiled samples. The decrease in crude fiber of cereals is may be due to the breakage of weak bonds between polysaccharide chains and glycosidic linkages in the dietary fiber polysaccharides (Ajala, 2009). The raw samples had significantly higher fiber content than heat treated samples. The same observation was reported by Luithui and Meera (2018) in adlai grain and by Chukwuma et al. (2016) in corn that the fiber content significantly decreases after heating.
In the same way, raw samples had the highest total ash content (0.38-1.64%) followed by boiled samples (0.25-0.41%) and the least in canned samples (0.21-0.38%). The reduction in ash content may be due to the leaching of microelements into the cooking water  (Myrene and D'souza, 2013).
Raw samples had the highest carbohydrate content and caloric value (80.42-83.92% and 382.09-383.48 kcal, respectively) followed by canned samples (19.59-35.39% and 121.99-201.76 kcal, respectively) while the boiled sample had the least carbohydrate content and caloric value (15.88-33.72% and 108-198.52%, respectively). Same observation by Kavitha and Parimalavalli (2014) that raw cereals contained higher carbohydrate content and caloric value than heat-treated samples.

Carbohydrate profile
Processing had a significant impact on the carbohydrate profile of adlai, OxL corn and adlai-corn blend as shown in Table 3. Boiling led to a significant (p<0.05) reduction in starch content of aldai, OxL corn and adlai-corn blend by 11.47%, 3% and 11.44%, respectively and by 12.28%, 4% and 12.11% after canning. Similarly, boiling significantly (p<0.05) decreased the amylose content of all the samples and further decreased by canning. However, starch and amylose values for boiled and canned samples were not significantly (p>0.05) different. Raw samples have significantly (p<0.05) higher starch and amylose content compared to heat-treated samples. During heat treatment, starch granules are gelatinized and partly solubilized (Pomeranz, 1990;Guillén et al., 2018) and these findings were supported by the study of Tester and Morrison (1993) that corn started swelling at around 40 o C and leaching of polysaccharides began. Hence, the decrease in starch and amylose may be observed. Same results were detected in the study of Luithui and Meera (2018) where the starch and amylose content of adlai decreases after subjecting to different temperatures.

Commercial sterility test for canning procedure
Some microorganisms that grow in canned foods do not produce gas and therefore cause no abnormal appearance of the packaging; nevertheless, they cause spoilage of the product. One of the reasons of spoilage is due to retort operations that are faulty because of inaccurate or improperly functioning thermometers, gauges, or controls (Landry et al., 2001)  broth did not exhibit turbidity or cloudy appearance. Hence, canned samples are safe from spoilage by thermophilic anaerobes such as C. thermobutylicum, C. botulinum, C. sporogenes, and C. perfringens. There was no presence of any microorganisms after the gramstaining was done.

Conclusion
The pure adlai, pure OxL corn and the 90% adlai:10% OxL corn were used in the study. Heat treatments were applied to the samples. Boiling made the texture of the cereals soft hence increases acceptability and palatability. Boiling and canning significantly (p<0.05) increased the moisture and fat content but significantly reduced the crude protein, crude fiber, total, carbohydrates, caloric value and carbohydrate profile of adlai, corn and adlai-corn blend. However, the difference between the values of boiling and canning were not significant (p>0.05).