Citation of this paper

Effect of drying method on the product quality and storage duration of cassava (Manihot esculenta Crantz) foliage

Nguyen Thi Bich Hanh^1,2, Bui Phan Thu Hang^1,2, Le Thi Thuy Diem^1,2, Vo Phuong Mai^1,2 and Vo Lam^1,2

¹ Department of Animal Sciences and Veterinary Medicine, An Giang University
² Vietnam National University Ho Chi Minh City, Vietnam
bpthang.agu@gmail.com

Abstract

The present study was conducted to evaluate the effect of drying procedures on quality and storability of cassava foliage. Sun dried or oven dried cassava foliage were preserved for 2, 4, 6, 8, 10, and 12 weeks in the polyethylene bags at room with temperature 28.4±0.8^oC and humidity 70.8±5.9%. The nutritive compositions and colour values were determined in the end of each period.

The results showed that the sun-dried cassava foliage reduced the crude protein content from 26.20-25.22%. The crude protein, fiber, lipid, and organic matter contents were not affected during preservation but the soluble protein content was declined after 12 weeks of storage. During storage, colour values L* and b* decreased, while a* increased in both sun dried and oven dried powered samples. In general, cassava foliage can be dried by sunlight and oven at 55^oC and storage until 12 weeks.

Key words: cassava foliage, colour, drying procedure, protein solubility, storage

Introduction

Cassava (Manihot esculenta, Crantz) is grown in the hilly and mountainous regions for foliage in the dry season in Vietnam. The area of cassava cultivation is around 532,600 ha per year, and can provide about 41 tones per ha of fresh leaves (GSO 2017; Dung et al 2005). Cassava foliage is by-product after tuber harvest and used successfully as a source of high protein in livestock and cricket production, with positive effects on their digestibility, performance and carcass properties (Wanapat 2001; Fasae et al 2011; Hue et al 2012; Nguyen et al 2012; Régnier et al 2013; Bui Phan Thu Hang et al 2020 and 2021). Casava foliage can decrease emission and methane production from ruminant production (Sangkhom et al 2017).

Processing method to preserve nutritive values of cassava foliage will play important role for suppling feed for livestock production during the dry season. Drying the cassava foliage is commonly used for preservation in Southeast Asia, which the cyanide acid (HCN) content can be decreased and size reduction (Wanapat and Kang 2013; Dung et al 2005). Sun drying is natural drying that has long been utilized for feed preservation technique due to using economical process. However, it is difficult to sun dry in the rainy season.

Therefore, this study was conducted to to evaluate the influence of sun drying and oven drying on nutritional and colour properties and preservation duration of cassava foliage.

Materials and methods

Sample preparation and drying process

Sweet cassava foliage (around 50 cm), with 80% leaves, 9% petioles and 11% fine stem in DM basis, was harvested in An Giang province, Vietnam and immediately brought to the laboratory. They were divided into two portions and cut with length 2-3 cm. Half of cut foliage was then dried at 55 ⁰C in an electric oven (Universal oven UF750, Memmert, Germany). Another portion was dried in sun drying with 31.9±1.5^oC and humidity 61.6±6.9%. The drying process lasted until the sample moisture content reached below 10% for inhibiting the present microbials (James and Kuipers 2003). The dried samples were ground at 300 μm sieve and packaged in a plastic bag (0.5 kg sample per each). Each drying method carried out eight replications (8 plastic containers). These containers were then stored at room with temperature 28.4±0.8^oC and humidity 70.8±5.9% for 2, 4, 6, 8 and 12 weeks for colour measurement and chemical analysis. Physicochemical properties were measured every two weeks.

Colour parameters

To evaluate three parameters (L^*, a^*,b^*) the samples were determined by using a portable colourimeter (CR-20 Chromometer, Konica Minolta, Japan). The L^* value ranges from 0 to 100 (black-white) which indicating the whiteness and blackness. The a^* and b^* measures the redness and greenness, and the yellowness and blueness which positive a^* and b^* values representing the redness and yellowness, respectively (CIE, 1978). Each sample was read in triplicate which taking randomly from different locations.

Chemical analysis

Samples were analysed for DM, CP, EE, CF and OM according to AOAC (2005). Protein solubility were determined by using the methodology described by Vojdani (1996).

Statistical analysis

The data from the experiment were subjected to analysis of variance using the General Linear Model (GLM) procedure of Minitab Software Release version 17 (2013).

Results and discussion

Chemical analysis of cassava foliage powder

The electric oven dried cassava foliage samples were found to have higher dry matter and crude protein contents (92.71% and 26,20%) than sun dried samples (91.64% and 25.22) (Table 1, p<0.05), respectively. The lower of crude protein content from the samples under the sun drying than the samples under the oven process might have been by the prolong drying procedure (13 hours and 11 hours for natural drying and oven drying, respectively), which caused loss of volatile nutrients from the sample (Abrol et al 2014). While soluble protein, organic matter, crude fat, and crude fiber contents of cassava foliage dried were similar results in both drying methods.

Table 1. Effect of drying methods on nutritional parameters of cassava foliage powder
Drying methods	DM	%DM basis
Drying methods	DM	CP	Protein solubility	EE	CF	OM

Sun drying	91.64^b	25.22^b	33.90	3.31	13.08	93.48
Electric oven	92.71^a	26.20^a	33.85	3.35	13.09	93.52

SEM	0.07	0.05	0.07	0.02	0.05	0.03
p	<0.01	<0.01	0.59	0.50	0.76	0.37
Means values within the same column with different superscripts differ at p<0.05

The dry matter and crude protein contents of samples gradually declined with the advancement of preservation period from 0 to 12 weeks (Table 2; Table 3; p>0.05). The decrease in dry matter content during preservation may be due to the water vapor permeability of container material. However, protein solubility content decreased around 3.8% and 7% in eighth and twelfth weeks, respectively, as compared to 0 week (Table 2; p<0.05).

Table 2. Effect of storage period on nutritional parameters of cassava foliage powder
Storage (weeks)	DM	%DM basis
Storage (weeks)	DM	CP	Protein solubility	EE	CF	OM

0	92.30	25.95	34.88^a	3.36	13.03	93.52
2	92.28	25.81	34.88^a	3.34	13.04	93.47
4	92.22	25.79	34.25^bc	3.35	13.08	93.50
6	92.22	25.70	34.02^cd	3.32	13.09	93.49
8	92.12	25.58	33.56^de	3.33	13.10	93.50
10	92.06	25.64	33.11^e	3.32	13.11	93.51
12	92.04	25.55	32.41^f	3.31	13.15	93.51

SEM	0.12	0.10	0.13	0.04	0.10	0.05
p	0.96	0.06	<0.01	0.83	0.99	0.99
Means values within the same column with different superscripts differ at p<0.05

The chemical properties of cassava foliage powers were not affected during storage in drying methods (Table 3; p>0.05). It was in good agreement with Ravindran (1993), who stated that nutritive quality of ground cassava leaves was maintained during preservation. However, it found that the protein solubility content of sun dried or oven dried cassava foliage samples tended to decline over 12 weeks of storage (p<0.05) and lower after 12 weeks of preservation. Insect infestations were not appeared after 12 weeks of preservation.

Table 3. Effect of drying methods and storage period on nutritional parameters of cassava foliage powder
Drying methods	Storage (weeks)	DM	%DM basis
Drying methods	Storage (weeks)	DM	CP	Protein solubility	EE	CF	OM

Sun drying	0	91.72	25.49	35.03	3.33	13.12	93.52
	2	91.73	25.28	34.85	3.32	13.06	93.42
	4	91.62	25.32	34.13	3.32	13.12	93.46
	6	91.62	25.18	34.16	3.31	13.04	93.47
	8	91.60	25.13	33.64	3.32	13.08	93.49
	10	91.62	25.14	33.25	3.30	13.10	93.48
	12	91.60	25.03	32.23	3.30	13.02	93.52

Electric oven	0	92.88	26.41	34.73	3.38	12.94	93.51
	2	92.83	26.33	34.92	3.36	13.03	93.51
	4	92.81	26.26	34.37	3.38	13.04	93.54
	6	92.83	26.22	33.88	3.33	13.14	93.51
	8	92.63	26.02	33.48	3.35	13.12	93.50
	10	92.51	26.14	32.96	3.34	13.10	93.55
	12	92.48	26.03	32.58	3.32	13.27	93.50

SEM		0.18	0.13	0.18	0.06	0.14	0.08
p		0.58	0.99	0.46	0.95	0.83	0.98

Colour measurements

The drying method had a strong effect on the lightness (L*), redness (a*), and yellowness (b*) values (Table 4, p<0.05). The lightness value of sun-dried cassava foliage (61.66) sample was higher than oven dried (60.79) sample (Table 4; p<0.05), meaning that sun dried sample was brighter than oven dried sample. Whereas, the a* and b* values were lower for sun dried (-18.82 and 18.04) sample than oven dried (-17.15 and 19.69) samples, respectively. These results indicated that the green and blue colours of cassava foliage powder were declined at oven drying, which probably due to the high oven drying temperature. According to Premi et al (2010) the a* value became more negative as drying temperature decreased.

Table 4. Effect of drying methods on colour parameters of cassava foliage powder
Drying methods	L^*	a^*	b^*

Sun drying	61.66^a	-18.82^b	18.04^b
Electric oven	60.79^b	-17.15^a	19.69^a

SEM	0.07	0.05	0.06
p	<0.01	<0.01	<0.01
Means values within the same column with different superscripts differ at p<0.05. L^: Lightness; a^: Redness; b ^: Yellowness.*

The rising of preservation period leaded to the decreasing of brightness and yellowness values but the advancement of redness values (Table 5; p<0.01). The brightness, and yellowness values for both sun dried and oven dried samples also declined with the increase of preservation period from 0 to 12 weeks (Table 6; p>0.05). However, redness value of sun dried as well as oven dried samples increased during storage period (p<0.05).

Table 5. Effect of storage period on colour parameters of cassava foliage powder
Storage (weeks)	L^*	a^*	b^*

0	62.91^a	-19.46^e	20.30^a
2	62.75^a	-19.34^e	20.24^a
4	61.61^b	-18.69^d	19.27^b
6	61.16^b	-18.15^c	18.73^c
8	60.41^c	-17.34^b	18.13^d
10	60.10^cd	-16.50^a	17.73^d
12	59.64^d	-16.39^a	17.63^d

SEM	0.13	0.09	0.12
p	<0.01	<0.01	<0.01
Means values within the same column with different superscripts differ at p<0.05. L^: Lightness; a^: Redness; b ^: Yellowness.*

Table 6. Effect of drying methods and storage period on colour parameters of cassava foliage powder
Drying methods	Storage (weeks)	L^*	a^*	b^*

Sun drying	0	63.35	-20.27^f	19.56
	2	63.10	-20.20^f	19.45
	4	62.19	-19.34^e	18.62
	6	61.70	-19.36^e	17.98
	8	60.80	-18.19^d	17.10
	10	60.41	-17.26^c	16.85
	12	60.09	-17.11^bc	16.70

Electric oven	0	62.48	-18.65^d	21.04
	2	62.39	-18.49^d	21.03
	4	61.04	-18.04^d	19.92
	6	60.62	-16.93^bc	19.49
	8	60.03	-16.49^b	19.16
	10	59.78	-15.75^a	18.60
	12	59.19	-15.68^a	18.57

SEM		0.19	0.14	0.17
p		0.78	<0.01	0.30
Means values within the same column with different superscripts differ at p<0.05. L^: Lightness; a^: Redness; b ^*: Yellowness.

Conclusions

The results showed that:

Cassava foliage can be dried both under sunlight and oven at 55^oC without much decrease in the proximate compositions.
Protein solubility declined as prolong storage duration.
The colour quality characteristics of casava foliage powders are not only depending on drying process but also storage period.

Acknowledgements

The authors are grateful acknowledge for the financial for this research from Vietnam National University Ho Chi Minh City (VNU-HCM) under grand number C 2021-16-01/HĐ-KHCN. We also acknowledge Ms. Em, and group of DH18CN, DH19TS students for their technical assistance.

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