Virology & Mycology Infectious Diseases

Search :   Advanced Search 

Home   |   Join   |   Contact     

   
Journal Details
 
Article usage
Total views: 0
[From(publication date):
-- May 26, 2013]
Breakdown by view type
HTML page views :
PDF downloads :
XML downloads :
 
 
Subscribe Here
Enter your name :*
Enter your Email : *
 
 
 
 
 
Research Article Open Access
Biotechnologically-Modified Cassava: Protein Absorption Relative to Casein
Xiangkai Li1*, Jian Yang2, Mark Manary2 and Kendal D Hirschi2,3
1Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, 730000, P.R.China
2United States Department of Agriculture/Agriculture Research Service, Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030
3Vegetable and Fruit Improvement Center, Texas A&M University, College Station, Texas 77845
*Corresponding author: Xiangkai Li
School of Life Sciences, Lanzhou University
Tianshui Nan Lu #222, Lanzhou, Gansu, 730000, P.R.China
Tel: 86-931-8912561
Fax: 86-931-8912560
E-mail: xkli@lzu.edu.cn
 
Received April 09, 2012; Accepted May 07, 2012; Published May 09, 2012
 
Citation: Li X, Yang J, Manary M, Hirschi KD (2012) Biotechnologically-Modified Cassava: Protein Absorption Relative to Casein. J Bioequiv Availab 4: 040-043. doi:10.4172/jbb.1000109
 
Copyright: © 2012 Li X, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
 
Abstract
 
Background: Biotechnology to increase the protein content of foods is an innovative strategy to address insufficient protein intakes. A novel biotechnologically modified cassava which has higher levels of protein than control cassava has been developed.
 
Objective: For dietary guidance, it is necessary to understand the relative servings of any specific product that would be needed to provide protein compared to a standard source, such as casein.
 
Methods: In a mouse feeding study we used weight gain to infer protein absorption from modified cassava (MOD) lines relative to control cassava lines (CON) and cassava fortified with casein (CON+casein).
 
Results: A pair feeding study demonstrated protein bioavailability in the MOD cassava was similar to the bioavailability of protein found in casein.
 
Conclusions: MOD cassava may be a means of providing protein to a large portion of the developing word. Further biotechnological enhancements of a range of foods may lead to substantial benefits in nutritional status for populations deficient in protein intake.
 
Keywords
 
Protein; Bioavailability; Biotechnology; Cassava
 
Abbreviations
 
MOD: Modified; CON: Control
 
Introduction
 
The biotechnological modification of plants to increase their nutritional benefits in the food supply is a rapidly expanding field of nutritional investigation [1-4]. The terms “biotechnology” and “genetically modified/enhanced” have been used to describe various strategies which implement some form of plant biochemistry modification. Modern biotechnology has been utilized in the United States food supply since the early1990s [5,6]. Currently, the majority of manufactured foods marketed in the United States contain modified soybean or corn ingredients (Institute of Food Technologists Expert Panel, 2000). Most crops are modified primarily for insect resistance or to improve tolerance to herbicides. However, increasingly, crops are being modified to enhance the nutritional profile of the plant in an effort to decrease nutritional deficiencies, promote health and wellbeing, and to enhance taste [7]. Modified plants have been analyzed for changes in plant metabolism and nutrient composition; however the functional outcomes related to their use has rarely been evaluated.
 
Increasing protein content in the diet of the malnourished is a challenging task [8]. Protein content in the human diet should be approximately 15% of total calories; however, in many areas of the world, including Africa, and southern Asia, the staple foods contain low levels of protein [9]. Thus the minimal levels of protein intake are not achieved and consequently health deteriorates [8,10]. Maximizing protein intake in impoverished areas of the world could dramatically improve the health status of millions of people.
 
Cassava (Manihot esculenta) is the third biggest carbohydrate source in the world and the fourth most important source of food energy in the tropics [11]. Cassava roots are not normally regarded as a good source of protein (3% in dry weight) [8,12,13]. A recent study among children that consume cassava as a staple food, found that 13% of Nigerian and 53% of Kenyan children had inadequate protein intake. The fraction of dietary energy derived from cassava was negatively correlated with protein intake, protein: energy (P:E) ratio, and dietary diversity. Height-for age Z score was directly associated with protein intake and negatively associated with cassava consumption [10].
 
Using biotechnology methods, modified cassava (MOD) accumulated zeolin within de novo protein bodies localized within the root storage tissues, which results in total protein levels of 12.5% dry weight within this tissue, a fourfold increase compared to CONs. There were no morphological alterations between transgenic and wildtype cassava, and no significant differences in average shoot or root yield, harvest index or dry matter and starch [9]. This work represents a proof of concept towards the potential transformation of cassava from a starchy staple, devoid of storage protein, to one capable of supplying inexpensive protein to a large portion of the world. However, no feeding studies have been done with the MOD plants to determine if this protein is bioavailable.
 
Rats and mice have been extensively used to study the efficacy of dietary regimes [14]. As in human diets, amino acids are a vital nutrient in rodent diets [15]. Limiting amounts of lysine, tryptophan and phenylalanine can suppress weight gain [16]. The National Research Council (NRC) has established guidelines for the amino acid content in mice diets. For example, lysine content is at 5.0 g/kg in diet, phenylalanine at 7.6 g/kg, and tryptophan at 1.0 g/kg [17]. Normal American Institute of Nutrition (AIN) mice diets contain 18% casein as the protein source [18]. Casein contains an excellent amino acid profile and is the predominant protein found in milk. For comparative purposes, casein has often been used as a standard protein source [19].
 
Here we tested the hypothesis that male mice consuming diets containing MOD cassava as the sole protein source will gain more weight than mice consuming diets containing control cassava. Furthermore, we tested the protein bioavailability in the MOD cassava relative to the bioavailability of protein found in casein. Our findings suggest that MOD cassava could be used to increase protein intake in vulnerable populations.
 
Materials and Methods
 
Mice strains
 
Animal protocols were approved by the Baylor College of Medicine Institutional Animal Care and Use Committee [20]. C57BL/6 (Charles River Labs, Wilmington, MA) mice were housed in cages with ad libitum access to water and food prior to the initiation of the experiment. Eighteen male weanling mice were used for this study.
 
Diet preparation
 
Cassava roots powders (Zeolin: protein enriched cassava (MOD); 60444: wildtype cassava (CON) ) were obtained from Claude Fauquet, Danforth center, St. Louis, MO. Lyophilized cassava was soaked in distilled water for 12 hours to remove the cyanogenic compounds and then lyophilized for 72 hours to obtain a powder [12]. In this study, cassava and casein were used as protein sources in the diets. Sucrose and other essential nutrients were added to the diets. The carbohydrate, fat, vitamin and mineral components in the formulated diets (Table 1) were similar to AIN93G and the fiber content was 8% in each diet. Sucrose and choline were purchased from Sigma (St. Louis, MO). Corn starch, corn oil, vitamin mix, and mineral mix were purchased from Dyets Inc. (Bethlehem, PA).
 
Table 1: The ingredients and calorie composition in three isocaloric diets.
 
Pair feeding study
 
The pair feeding study was carried out using a Comprehensive Lab Animal Monitoring System (CLAMS; Columbus Instruments, Columbus, OH, [21,22]). The eighteen male weanling mice were allotted into one of three different diets using a randomized block design. Mice were habituated to the CLAMS cage for 48 hours prior to the 14-day experiment. Diets were distributed using a CLAMS feeder where we monitored the mass of food removed from the container that resided on a precision balance. Water was allowed ad libitum throughout the experiment and acclimation process. The CON fed mice were the master group while mice eating CON+casein and MOD could not consume diets exceeding the average diet consumed in the CON group. The food intake of the mice eating CON cassava was monitored every hour, and this quantity of food was then given to the mice eating both the MOD cassava and the cassava supplemented with casein. Individual bodyweight gains were recorded every 24 hours.
 
Statistical analysis
 
The Statistical analysis was done by SPSS Version 11. T-test among three groups was conducted and subsequent pairwise comparisons were performed with Sidak multiple comparison test.
 
Results
 
In agreement with previous studies, we found that when mice are given standard 4% protein diets, male mice’s body weights are stable while for females the protein needed is 6%. This could be a result of male mice eating on average 3.1 g of diets per day and female mice consuming only 2.6 g (data not shown). When the control (CON) cassava is used as the sole protein source it did not contain enough protein to facilitate growth (Figure 1, Table 2).
 
Figure 1: Weight gains of weanling mice fed with three isocaloric diets over 14 days.
 
Table 2: The measurement of weight and weight gain of weanling mice in three feeding groups.
 
The mice ingesting CON cassava diets sustained a weight loss during the 14-day experiment (Figure 1, Table 2). In contrast, the bodyweight of the mice ingesting the MOD cassava or the cassava supplemented with casein (CON+casein) increased in a similar manner throughout the experiment (Figure 1, Table 2). Diet intake records confirmed that all mice consumed similar amounts of the diets (Figure 2). The growth of the MOD and CON+casein consuming mice was visually obvious after the two-week period whereas the CON consuming mice were smaller than at the beginning of the two-week dietary regime (Figure 3). Differences with respect to final-initial weight change between MOD and CON mice, or between CON+casein and CON mice, were 5.03 g and 5.63 g, respectively, which were significant at p<0.001 by pairwise comparisons using the Sidak multiple comparison procedures. The difference of final-initial weight between MOD and CON+casein is 0.63 g, which was not significant (p = 0.234) at the current sample size (Table 2).
 
Figure 2: Diets intake of weanling mice groups fed with three different isocaloric diets.
 
Figure 3: Visual comparison of weanling mice fed with three isocaloric diets, before/after the 14-day period.
 
Our results indicate that when used as sole protein source, CON cassava would not support weanling mice growth while the MOD cassava diets contained adequate levels of protein to support growth. Our initial studies suggest that the protein bioavailability of the modified cassava may be similar to the protein found in casein.
 
Discussion
 
Control cassava roots (CON) contain 3% protein by dry weight which is insufficient when used as the sole protein source in mouse diets. In this work, we have shown that protein enriched cassava (MOD) that contain 12% protein in dry weight can support weight gain in a similar manner to CON cassava supplemented with casein (CON+casein).
 
The protein in the MOD cassava appears to be similar in quality to casein. Casein is a slow-digesting natural protein derived from dairy sources. Milk is about 80%casein. An attractive property of the casein molecule is its ability to form a gel or clot in the stomach, which makes it very efficient in nutrient supply [23]. Our results here suggest that the protein in the MOD cassava might have many of the same general properties as the protein found in casein.
 
The CLAMS system, while expensive to operate, does allow access to the food to be placed under automatic computerized control. In this way, we were able to precisely monitor the food intake among the mice and ensure that no differences were due to the amount of the diets consumed. For cost purposes, these precise feeding studies were done using a sample size of six in each group for a period of two-weeks. However, we obtained similar results using a non-automated feeding system where we analyzed an additional 20 animals on each diet for three-weeks (data not shown).
 
Cassava has the lowest protein:energy ratio (P:E) of any staple food, with protein content ranging from 1-3% dry weight [8,11]. Thus, a small child consuming 50% of his/her dietary energy as CON cassava will receive about 5 g dietary protein, equivalent to 35% of their daily protein requirement [9]. The same child consuming the same amount of modified cassava accumulating storage protein at levels achieved in the present study would obtain approximately 18 g of dietary protein, or more than 100% of their daily requirement. This illustrates that MOD cassava could be a potentially important component of delivering enhanced nutrition to at-risk populations.
 
Conclusions
 
Our results show that, in the previously developed MOD cassava, the enriched zeolin protein content has similar quality and bioavailability to those of casein, which supports the weight gain of weanling mice. Our work here provides a foundation for further testing and use of this valuable biotechnologically modified food species. Further biotechnological enhancements of a range of foods may lead to substantial benefits in nutritional status for populations deficient in protein intake.
 
Acknowledgements
 
We thank Claude Fauquet for the cassava. Funding for this work was supplied by grants from Lanzhou University, lzujbky-2011-32 to X. Li and from the National Institutes of Health No. IR01 DK 062366 and USDA CSRESS#2005-34402-16401 Designing Foods for Health, both to K. Hirschi.
 
References
 























 
 
 
This article
DOWNLOAD
» XML (89 kB)
» PDF (1,211 kB)
»
Export citation
x
»
Blog this article
   
CONTRIBUTE
» Write a response
» Read other responses
» Publishing with OPG
   
SHARE
» E-mail this article
» Print this article
» Rights and permissions
   
Share
EXPLORE
Related article at
» Pubmed
» DOAJ
» Scholar Google
 
 
 
 
Untitled Document
| More
 
OMICS Publishing Group is the member of / publishing partner of/source content provider to
       
OMICS Publishing Group, An Open Access Publisher and Scientific Events Organizer for the Advancement of Science & Technology. All Published content, except where otherwise noted, is licensed under a Creative Commons Attribution License
Please ensure that you are using the latest version of Adobe reader. If you do not have this software installed on your system, you can download the free Adobe Reader by simply clicking on the following link: http://www.adobe.com/products/acrobat/readstep2.html
Best viewed in Mozilla Firefox | Google Chrome | Above IE 7.0 version Copyright © 2013 OMICS Group, All Rights Reserved.