Luận án Nutritive improvement of cassava root and its utilisation in taro foliage and banana stems basal diets for local pig production in smallholders in lao PDR

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CHAPTER 2
IMPROVING NUTRITIVE VALUE OF CASSAVA ROOTS 
(Manihot esculenta Crantz)
ABSTRACT
Two experiments were carried out to study: (experiment 1) Cassava root was fermented with yeast, urea and di-ammonium phosphate (DAP) in a solid-state fermentation to determine the degree of conversion of crude to true protein; and (experiment 2) the limiting factor to the synthesis of true protein from crude protein in the fermentation of cassava root could be the decrease in pH in the fermentation substrate preventing the hydrolysis of urea to ammonia and thus decreasing the availability of nitrogen for growth of the yeast. The following experiment to determine the degree of conversion of crude to true protein, pH and ammonia. In experiment 1. The experiment was arranged as a 2*3*4 factorial in a completely randomized design (CRD). The treatments were: root processing: steamed and not steamed; DAP: 0, 1 and 2% of the substrate DM. The fermentation was over 14 days with samples taken for determination of true and crude protein at 0, 3, 7 and 14 days. In experiment 2 a completely randomized design (CRD) was used with 2 treatments arranged as a 2*9 factorial. The treatments were anaerobic and aerobic fermentation. The substrate was cassava root 93.6% + di-ammonium phosphate (DAP) 2% + urea 1.4% + yeast 3​% (DM basis). True, crude protein, ammonia and pH were measured at 0 and 3h after preparing the substrates and every 24h until end of day 7 (0, 3h, 1, 2, 3, 4, 5, 6 and 7 day).
Experiment 1. The true protein in cassava root increased with a curvilinear trend (R2 = 0.98) from 2.30 to 6.87% in DM as the fermentation time increased from zero to 14 days; the ratio of true to crude protein increased from 24.6 to 63.7 over the same period. Increasing the proportion of DAP from zero to 2% of the substrate DM increased the true protein from 5.6 to 7.3% in DM after 14 days of fermentation. Steaming the cassava root prior to fermentation improved slightly (p=0.67) the conversion of crude to true protein.
Experiment 2. The pH decreased with fermentation time, according to an almost linear trend, from 5.8 immediately after mixing the substrate, to 5.47in 3h and to 3.43 after 7 days. The level of crude protein after mixing the substrate and additives was 10.35% in DM and did not change over the 7 days of fermentation. True protein in the substrate increased from 2.37 to 6.97% in DM as the fermentation time increased from zero to 7 days. There were no differences in all these criteria as between the aerobic and anaerobic condition, other than a tendency for the pH to fall slightly more quickly in the first 4 days in the anaerobic condition followed by a slower rate of fall to reach almost the same final value after 7 days, as for the aerobic condition. It is suggested that the incomplete conversion of urea-N and ammonia-N to yeast protein was because of incomplete hydrolysis of urea to ammonia due to action of urease being inhibited by the fall in pH during the fermentation.
Key words: ammonia, pH, true protein, crude protein, steaming
INTRODUCTION
The major problems of small-holder pig production in upland areas of Lao PDR are high piglet mortality and low growth rates. Almost all pigs are of local breed (Moo Lath), managed in scavenging systems and suffer feed inadequacy in both quality and quantity. According to the survey by Phonepaseuth et al., (2010) most piglets in upland areas had a low growth rate (20-50 g/day) and high mortality (30-50%). Weaned pigs required from 5 to 8 months to reach live weights of 20 to 30 kg.
In Laos, cassava (Manihot esculenta Crantz) known as ‘Man Ton’ is one of the main food crops for smallholder farmers in remote upland areas, and it is currently the second most important crop after rice. Recently, the crop has become an important cash crop for either domestic use or for export because it can be used for food and feed as well as for industrial processing into starch, sweeteners and ethanol. Cassava farms are needed not only for food crops but more importantly as a major source of income for rural households. The cassava root is composed of carbohydrates and is therefore mainly a source of energy. The starch content varies between 32 to 35% of the mass of fresh root and 80 and 90% of the mass of dried roots (Montagnac et al., 2009). The protein content is trivial, between 1 and 3% of dry matter (Buitrago, 1990) and about 1.5mg/100 g of fresh mass (Bradbury and Holloway, 1988). Essential amino acids are present in low quantities, with the exception of arginine, glutamic acid and aspartic acid (Gil and Buitrago, 2002). 
Solid state fermentation of the root is a promising technology as this has the potential to raise the protein content to levels required to balance the carbohydrate thus presenting the opportunity to make an almost complete feed for monogastric animals such as pigs and poultry (Boonnop et al., 2009; Kaewwongsa et al., 2011). 
One way to improve the protein content of carbohydrate-rich feeds is by solid-state fermentation with fungi and yeasts (Araujo et al., 2008; Hong and Ca, 2013).  The fermentation of cassava meal with S. cerevisiae enhanced the protein level from 4.4% to 10.9% in DM and decreased the cyanide content (Oboh and Kindahunsi, 2005).
Solid state fermentation of the root with urea and di-ammonium phosphate (DAP) is a promising technology as this has the potential to raise the protein content to levels required to balance the carbohydrate, thus presenting the opportunity to make an almost complete feed for monogastric animals such as pigs and poultry (Boonnop et al., 2009).
The problem, in the studies reported so far, is that not all the added nitrogenous compounds (urea and DAP) were converted to “true” protein, the levels of which never exceeded some 50 to 70% of the “crude “ protein in experiments with yeast-fermented cassava root (Vanhnasin and Preston, 2016a) and cassava root pulp (Sengxayalth et al., 2017a). Yeast cannot directly use urea which must first be hydrolysed to ammonia by urease. However, the activity of urease is inhibited at low pH (Kay and Reid, 1934), which falls rapidly when the cassava root is fermented. 
EXPERIMENT 1: 
MATERIALS AND METHODS
Location
The experiment was carried out in the Laboratory of the Animal Science Department in the Faculty of Agriculture and Forest Resource in Souphanouvong University. The site is located 7 km from Luang Prabang City, Lao PDR. The mean daily temperature in this area at the time of the experiment was 27oC (range 22-32°C).
Experimental design
The experiment was arranged as a 2*3*4 factorial in a completely randomized design (CRD) with 4 replications in each period.
The treatments were:
Root processing
Steamed (ST) and not steamed (NST)
Di-a