Food Chemistry 145 (2014) 372–377

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Characterisation of a novel softened rice product Masahiro Hayashi ⇑, Kumiko Kato, Shingo Umene, Hiroaki Masunaga Tokyo Laboratory, EN Otsuka Pharmaceutical Co., Ltd., Japan

a r t i c l e

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Article history: Received 21 March 2013 Received in revised form 14 August 2013 Accepted 16 August 2013 Available online 27 August 2013 Keywords: Cooked rice Enzymatic treatment Texture Digestibility Molecular weight distribution

a b s t r a c t We developed a novel softened rice by permeating rice with enzymes that catalyse its decomposition. Herein, we characterised the softened rice (SR) and compared it to normal cooked rice (CR) and rice gruel (RG). SR resembled CR but not RG in appearance. Texture analysis showed that SR was the least firm, adhesive, and cohesive of the three rice preparations. SR contained almost the same amount of nutrition per unit mass as CR and twofold as much as RG. Analysis of digests of energy-equivalent amounts of the three rice preparations indicated that SR digests had the lowest quantity of residue and highest quantity of dissolved carbohydrate, maltose and glucose. The molecular weight (MW) range of SR constituents was 103–105, whilst those of CR and RG constituents were mainly 105–106. These results suggested that enzymatic decomposition of SR improves ease of eating, nutrition value, and digestibility at once. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Hospitals and nursing homes in Asian countries including Japan usually provide rice gruel (cooked with a lot of water to make rice easier to eat and digest) to elderly people and other patients (Kim, Kim, & Lee, 2010; Kohyama et al., 2005; Onitsuka, Toda, Kasai, & Hatae, 2003). However, too much rice gruel must be ingested to equal the energy provided by an ordinary meal, because the nutrients in rice gruel are diluted 2–5 times (Kohyama, 2003; Kohyama et al., 2005). Therefore, most elderly people and other patients need nutrients from other sources such as nutrient infusion and enteral nutrition, which may constitute a burden. Oral Nutritional Supplements (ONS), which are liquid foods, have been developed as a means of artificial nutritional support and used to improve nutritional intake in elderly people and patients with malnutrition (Nieuwenhuizen, Weenen, Rigby, & Hetherington, 2010). In another study, carbohydrate rich supplement of ONS was provided for patients with chronic obstructive pulmonary disease (Steiner, Barton, Singh, & Morgan, 2003). The supplemented patients gained weight and their exercise performances were improved, compared with the non-supplemented. These suggested that ONS were helpful for elderly people and patients, especially those rich in carbohydrates. Studies on enzymatic treatment of rice were reported previously. Instant rice porridge produced by enzymatic treatment including a-amylase, b-amylase and neutral protease and drying ⇑ Corresponding author. Present address: Tokyo Laboratory, EN Otsuka Pharmaceutical Co., Ltd., 1-11-10 Kinshi, Sumida-ku, Tokyo 130-0013, Japan. Tel.: +81 3 5610 8551; fax: +81 3 5610 8557. E-mail address: [email protected] (M. Hayashi). 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.08.067

methods (Deng, Wang, Wang, Zhou, & Xiao, 2012). A method was proposed to produce hypoallergenic rice by carbonate (pH 9) containing glycerin monooleate and Actinase for patients with rice allergy (Watanabe et al., 1990). Moreover, using pancreatin and diastase, cooked rice suitable for aged people and adult disease patients was investigated (Tajiri, 1995). We applied the technology of permeating foods with enzymes to rice and produced a novel softened rice product with the same nutritional value, taste, and appearance as cooked rice (Hayashi, Kuribayashi & Sugimura, 2010). In this report, we compared the appearance, texture, nutritional value, digestibility, and molecular weight distribution of starch of the softened rice (SR) product to those of ordinary cooked rice (CR) and rice gruel (RG).

2. Materials and methods 2.1. Sample The SR product was prepared using an enzyme permeation method (Hayashi et al., 2010) as follows. Polished koshihikari rice (1.4 kg) was immersed for an hour in 1st enzyme solution (5.5 kg) containing 0.030% (w/w) citric acid, 0.10% (w/w) sodium citrate, 0.028% (w/w) a-amylase from Bacillus sp. (NAGASE & Co., Ltd., Osaka, Japan), 0.099% (w/w) papain from Carica Papaya (Amano Enzyme Inc., Aichi, Japan) and 0.028% (w/w) hemicellulase from Aspergillus niger (Amano Enzyme Inc.), taken out of the solution and heated with steam for 15 min. The rice was immersed in the 1st enzyme solution again, and cooked for 85 min, as the temperature rose from 78 to 99 °C. Then, 2nd enzyme solution (150 g) containing 0.030% (w/w) citric acid, 0.25% (w/w) sodium citrate,

M. Hayashi et al. / Food Chemistry 145 (2014) 372–377

and 0.025% (w/w) a-amylase from Bacillus sp. (NAGASE & Co., Ltd.) was added to the cooked rice. The cooked rice was divided into a small portion, heated at 90 °C for 40 min, and frozen at 35 °C for an hour. The defrosted product SR was compared to a readyto-use cooked rice product ‘‘Sato no gohan’’ (CR; Sato Foods Co., Ltd., Niigata, Japan) after warming with microwave, and rice gruel (RG), which was prepared by immersion of koshihikari rice (140 g) in five volumes of water (700 g) and cooking in an electric rice cooker. 2.2. Texture analysis Texture analysis was performed using a Creepmeter RE2–33005B (Yamaden Co., Ltd, Tokyo, Japan) at two temperatures 20 ± 2 °C and 45 ± 2 °C in accordance with a previously described method of testing food for people with difficulty in swallowing (Ministry of Health, Labor and Welfare, Japan, 2009). A sample was placed in a Petri dish (40 mm in diameter and 15 mm in height) and vertically compressed twice with a plastic plunger (20 mm in diameter) to a depth of 5 mm from the bottom of the dish. The speed of the plunger movement was 10 mm/s. From the curve obtained, firmness, adhesiveness, and cohesiveness were calculated (Kohyama et al., 2005; Onitsuka et al., 2003). 2.3. Nutritional analysis The content of moisture, protein, lipid, and ash in each sample was measured using the air-oven method (AOAC, 2002), Kjeldahl method (Kjeldahl, 1883), acid hydrolysis method (AOAC, 1980), and direct ashing method (AOAC, 2002), respectively. Each measurement was repeated three times and the average and standard deviation were calculated. The carbohydrate content was calculated as follows: Carbohydrate = 100 (moisture + protein + lipid + ash). Energy was calculated using following coefficients: protein, 16.736; lipid, 37.656; carbohydrates, 16.736 (Atwater, 1910; FAO/WHO, 1973). 2.4. Artificial digestion test Artificial gastric juice was prepared by dissolving pepsin (4 g/L; Nacalai Tesque; Kyoto, Japan) in disintegration test solution 1, pH 1.2 (Kanto Chemical, Tokyo, Japan) and the artificial intestinal juice was prepared by dissolving pancreatin (10 g/L; Wako Pure Chemical Industries, Osaka, Japan) in disintegration test solution 2, pH 6.8 (Kanto Chemical) (Kanaya & Sato, 2012). Each sample (CR 34 g, RG 78 g, and SR 40 g, the mass calculated based on an energy equivalent of 209 kJ) was digested in a 500-mL beaker containing 250 mL of one of the juices at 37 ± 1 °C in a water bath with stir-bar stirring. After 5, 10, 30, and 60 min of digestion, the samples were filtered through a 2-mm sieve and their residues were collected and weighed. 2.5. Quantitative analysis of carbohydrate The liquid portion of each sample (free of residue) was centrifuged at 15,000g for 10 min, and the supernatant was passed through a 0.45-lm filter. The filtrate was assayed using the phenol–sulphuric acid method (Hodge & Hofreiter, 1962). Soluble carbohydrate concentration was calculated from a glucose calibration curve. 2.6. Quantitative analysis of maltose and glucose The liquid portion of each sample (free of residue) at 5 and 60 min of digestion was adjusted to approximately pH 8 with 1 mol/L sodium hydrate, boiled for 5 min, centrifuged at 15,000g

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for 10 min, and the supernatant was passed through a 0.45-lm filter. The filtrate was assayed by Sucrose/D-Glucose/D-Fructose UV method kit (R-Biopharm AG, Darmstadt, Germany). 2.7. Molecular weight (MW) distribution analysis Samples were ground with a mortar and pestle, suspended in dimethyl sulfoxide (DMSO) (Zhong, Yokoyama, Wang, & Shoemaker, 2006) with 50 mmol/L LiCl so that the carbohydrate content was 1 g/L, incubated at room temperature overnight to dissolve the carbohydrate, and filtered through a 0.5-lm filter. The filtrate (20 lL) was injected into a gel permeation chromatography (GPC) system (HLC-8220GPC; Tosoh Corporation, Tokyo, Japan) equipped with two TSKgel super AWM-H columns (6 mm I.D.  15 cm; Tosoh Corporation) and a differential refractometer as a detector. The conditions were as follows: eluent, DMSO with 50 mM LiCl; flow rate, 0.6 mL/min; column temperature, 40 °C. Standard pullulan (Showa Denko K. K., Tokyo, Japan) was used as the standard molecular weight marker. 2.8. Statistical analyses Assuming normality in the population of all groups, SR was compared with CR and RG using Welch’s t test. The statistical significance level was set at p < 0.05. 3. Results and discussion 3.1. Appearance The appearance of the samples was compared (Fig. 1). Although RG was fluid and consisted of hard-to-recognise grains, SR and CR consisted of similarly clear and easily recognizable grains. The appearance of foods is recognised as an important attribute, and mashed foods or jellied foods dominate the food supply in hospices, but some of them are not liked by the elderly patients (Nishinari, 2004). For the reason, SR is assumed to be preferred as much as CR by elderly patients. 3.2. Texture analysis The results of the texture analysis can be used to evaluate ease of eating (Table 1). The firmness of SR was less than 1/3 that of CR and that of RG and was independent of the temperature. The chewiness of instant rice with enzymatic treatment was about 23% lower than that of control rice (Tajiri, 1995). These results suggested that the difference between the treatment of SR and the instant rice such as enzyme type, method for adding enzyme, and condition of reaction changes the firmness of rice, and SR is softer and more suitable for elderly people and patients. The firmness of CR and RG increased by more than 50% and that of SR by only 10% when temperature was changed from 45 to 20 °C, which means the firmness of SR was less affected by change in temperature. SR is expected to remain soft despite a drop in temperature during the meal. The adhesiveness of SR was less than 1/3 that of CR and 1/7 that of RG, regardless of the temperature, though the stickiness of the instant rice with enzymatic treatment was less 11% lower than control rice (Tajiri, 1995). Highly-adhesive triturated food requires more forceful movements of tongue to form a bolus just before swallowing (Shiozawa, Kohyama, & Yanagisawa, 1999). Hence, SR could need weaker movement of tongue and be easier to swallow, compared with the instant rice. Similarly, the cohesiveness of SR was 0.05–0.1 less than that of CR and RG, which meant that SR would be crumblier and melt in the mouth more easily. Thus, the

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Fig. 1. Appearance of the samples.

Table 1 Texture analysis of the samples.a Sample

Firmness

Adhesiveness

20 °C 4

45 °C

20 °C

2

2

10 N/m CR RG SR a

5.2 ± 1.9 1.9 ± 0.7 1.1 ± 0.1

10 J/m 3.2 ± 0.2 1.2 ± 0.1 1.0 ± 0.1

Cohesiveness 45 °C

20 °C

45 °C

12.9 ± 2.4 23.2 ± 3.3 3.2 ± 0.6

0.44 ± 0.02 0.45 ± 0.01 0.39 ± 0.04

0.47 ± 0.03 0.50 ± 0.02 0.38 ± 0.01

3

14.5 ± 2.3 25.4 ± 2.0 3.8 ± 0.8

n = 5, mean ± SD. All differences between SR and the other rice preparations were significant (p < 0.05).

Table 2 Nutritional analysis of the samples on an as-is basis.a Sample

Protein g/100 g

Lipid

Carbohydrate

Moisture

Energy kJ/100 g

CR RG SR

2.24 ± 0.01* 0.96 ± 0.01* 2.13 ± 0.00

0.353 ± 0.02 0.190 ± 0.04* 0.353 ± 0.02

33.2 ± 0.03* 14.5 ± 0.06* 27.8 ± 0.23

64.1 ± 0.05* 84.3 ± 0.10* 69.7 ± 0.24

607 ± 1.10* 265 ± 2.05* 513 ± 4.14

a *

n = 3, mean ± SD. Significantly different from SR (p < 0.05).

texture of SR was found to be appropriate for elderly people and patients.

treated with fluid restriction from cirrhosis and kidney disease, because of the small moisture content. 3.4. Residue weight after artificial digestion

3.3. Nutritional analysis The content of the three major nutrients, moisture and energy content on an as-is basis is shown in Table 2. The protein content of SR was equal to that of CR and double that of RG. Rice has low lipid content, and so all samples contained only 0.19–0.35 g/ 100 g. The carbohydrate and energy contents of SR (27.8 g/100 g, 513 kJ/100 g) were slightly less than those of CR (33.2 g/ 100 g, 607 kJ/100 g) but twice those of RG (14.5 g/100 g, 265 kJ/100 g). The energy content of the instant rice with enzymatic treatment (572 kJ/100 g) was almost same as that of the control rice (578 kJ/100 g) (Tajiri, 1995). The enzymatic treatment of SR was thought to be severer and lose more energy content from rice than that of the instant rice. On the other hand, the moisture of SR was a little more than that of CR and less than that of RG. Hence, SR contained a little less nutritional value of CR but about twice that of RG. For elderly people and patients, large portions may be overwhelming and may actually discourage intake (Huffman, 2002). In addition to the result of texture analysis, these results indicated that providing SR would lighten mental and physical burdens for the people who take rice gruel on a daily basis, because only half volume of SR as against rice gruel was needed to achieve the same target intake. And also, SR could be available for people who were

The digestibility of the samples with the same energy content (Fig. 2) was examined. During gastric juice digestion, the residue weight of CR increased about 10 g up to 5 min of digestion time, but then remained the unchanged thereafter. CR seemed to absorb the juice and swell without being digested, because the influence of mastication with saliva containing amylase in the mouth was not included in this test. In contrast, those of SR and RG decreased with the digestion time. It was understood that the better digestibility of SR and RG was attributed to the enzymatic treatment of SR and the cooking with much water of RG respectively. Finally, that of SR reached its nadir (approximately 19 g) after 60 min of digestion. As in gastric juice digestion, intestinal juice digestion resulted in increased residue weight of CR after 5 min of digestion, but then in slightly decreased residue weight. On the other hand, the weights of SR and RG decreased over time of digestion in intestinal juice in the same way as in gastric juice. However, the decrease was more marked in intestinal juice than in gastric juice. The residue weight of SR fell to its nadir (approximately 7 g) at the end of the intestinal juice digestion as in gastric juice digestion. The different result between the gastric and intestinal juice was associated with enzyme activities of the juices. Whilst the gastric juice included only protease of pepsin, the intestinal juice was

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80

CR

Residue weight (g)

70

B

60

SR

50 40

30 20

80 CR

70

RG Residue weight (g)

A

RG

60

SR

50 40 30 20 10

10

0

0 0

15

30 45 Digeson me (min)

0

60

15

30 45 Digeson me (min)

60

Fig. 2. Residue weight after digestion. (A) Gastric juice and (B) intestinal juice. n = 3, mean ± SD. All differences between SR and the other rice preparations were significant (p < 0.05).

A

B

50

50

CR SR 30 20

Carbohydarte (g/L)

Carbohydrate (g/L)

40

RG

40

30 20

10

10

0

0

0

15

30

45

60

Digeson me (min)

CR RG SR 0

15

30

45

60

Digeson me (min)

Fig. 3. Amount of carbohydrates in the digestive juices. (A) Gastric juice and (B) intestinal juice. n = 3, mean ± SD. All differences between SR and the other rice preparations were significant (p < 0.05).

added with pancreatin having many activities such as protease, lipase, amylase, and so on. Then, the intestinal juice digested the samples better. A low residue diet was comparable to a clear liquid diet for bowel preparation without increased side-effects, and post-gynecological surgery, early feeding using low residue diet decreased nausea without increasing gastrointestinal symptoms when compared to the traditional feeding method (Ong, Ong, & Han, 2012). For the good digestibility, SR could be used as low residue diet in the perioperative of gastrointestinal conditions. 3.5. Amount of carbohydrate in the juices The amount of carbohydrate dissolved in the juices is shown in Fig. 3. In gastric juice, although the amounts of carbohydrate in CR and RG hovered at about 0 g/L, that in SR went over 20 g/L at 5 min of digestion, reached about 27 g/L at 15 min and remained at that level thereafter. In intestinal juice, carbohydrate amounts increased in all samples as digestion progressed. Those in CR, RG, and SR respectively reached 23, 26, and 43 g/L at the end. Thus, as with gastric juice digestion, the intestinal juice digestion of carbohydrate was the most extensive in SR. Although the residue weights of SR and RG decreased in the same way during digestion, the amount of carbohydrate in SR was more than that in RG, especially in gastric juice. It was anticipated that the enzymatic treatment of SR was effective to disperse and dissolve rice grains in the juices, whilst the cooking with much water of RG was effective only to disperse. Rice contained substantial amounts of slowly

digestible starch (Aarathi, Urooj, & Puttaraj, 2003), but a part of slowly digestible starch of SR can be degraded during the process and easier to dissolve. 3.6. Amount of maltose and glucose in the juices The amount of maltose and glucose dissolved in the juices at 5 and 60 min of digestion is shown in Table 3. In gastric juice, maltose and glucose in CR and maltose in RG at both times were not detected, and there were 0.04 g/L of glucose in RG. The amount of maltose in SR increased from 0.54 g/L at 5 min of digestion to 0.68 g/L at 60 min, and the amount of glucose slightly went up from 0.14 g/L at 5 min to 0.15 g/L at 60 min. In intestinal juice, the amount of maltose and glucose in all the samples rose from 5 to 60 min of digestion. Especially, the amounts of maltose in intestinal juice was much more than those in gastric juice, and those in CR and RG reached over 10 g/L and that in SR got to 23.9 g/L at 60 min of digestion. Maltose and glucose are absorbable in the intestine (Holmes, 1971). SR is expected to be not only digested but absorbed in the body smoothly and be useful as a carbohydrate source. 3.7. MW distribution analysis The distribution of molecular weights in the samples is shown in Fig. 4. The main peak of CR was in the MW range of 105–106. The two peaks of RG were the big one in the MW range of

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Table 3 Amount of maltose and glucose in the digestive juices.a Digestion time

CR

RG

Maltose

SR

Glucose

Maltose

Glucose

Maltose

Glucose

g/L Gastric juice 5 min 60 min

N.D. N.D.

N.D. N.D.

N.D. N.D.

0.04 ± 0.00 0.04 ± 0.01

0.54 ± 0.06 0.68 ± 0.04

0.14 ± 0.01 0.15 ± 0.01

Intestinal juice 5 min 60 min

2.70 ± 0.30 11.4 ± 1.40

N.D. 0.17 ± 0.09

5.52 ± 0.39 11.5 ± 1.08

N.D. 0.01 ± 0.01

11.6 ± 3.49 23.9 ± 2.08

0.27 ± 0.05 0.61 ± 0.07

N.D. not detected. a n = 3, mean ± SD. All differences between SR and the other rice preparations were significant (p < 0.05).

100

Differenal Distribuon Value

90

CR

RG

SR

80 70 60 50 40 30 20 10 0 0

1

2

3

4

5

6

7

8

Log[MW] Fig. 4. Molecular weight distribution.

105–106 and the small one in the range of 101–103. Rice originally contains 10 types of a-amylase which have different characters (Mitsui, Yamaguchi, & Akazawa, 1996). The small peak of RG might be generated by amylase from rice itself, because the cooking with much water of RG can use more water to hydrolyse with the enzymes, compared to CR. The three main peaks of SR were MW 103, 104, and 105 and the distribution was more even in the range MW 103–105. The enzymatic treatment of SR decomposes the structural molecules including starch of rice to smaller ones, which could result in the ease of eating and digesting. 4. Conclusions The novel softened rice that we developed has the same appearance as normal cooked rice, twice the nutritional value of rice gruel, greater edibility and digestibility, compared with normal cooked rice and rice gruel. We attribute the characteristics of SR to the enzymatic conversion of rice constituent to smaller carbohydrate molecules. Moreover, we expect that SR will help to extend the range of oral nutrition options and establish new nutritional strategies, because of the characteristics not present in normally cooked rice. References AOAC. (1980). Official methods of analysis of AOAC (13th ed.). Washington, DC: Association of Official Analytical Chemists. AOAC. (2002). Official methods of analysis of AOAC (17th ed.). Washington, DC: Association of Official Analytical Chemists.

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Characterisation of a novel softened rice product.

We developed a novel softened rice by permeating rice with enzymes that catalyse its decomposition. Herein, we characterised the softened rice (SR) an...
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