Effect of sulfur concentrations in fermented total mixed rations containing fresh cassava root on rumen fermentation

2020 ◽  
Vol 60 (11) ◽  
pp. 1429 ◽  
Author(s):  
Chanadol Supapong ◽  
Anusorn Cherdthong

Context Feeding of fresh cassava root in ruminants is limited because it contains a high level of hydrocyanic acid (HCN), which is responsible for poisoning. Aims The objective of the present study was to evaluate the effect of sulfur levels supplementation in the fermented total mixed ration (FTMR) containing fresh cassava root as an energy source on the gas kinetics, ruminal fermentation, reduction of HCN concentration and nutrient digestibility in the in vitro gas production. Methods The experimental design was a 3 × 4 factorial in a completely randomised design. Dietary treatments contained factor A, which was three levels of sulfur supplementation at 0, 1 and 2% in FTMR, and factor B was ensiling time at 0, 7, 14 and 21 days respectively. Key results Concentration of HCN in FTMR was significantly reduced (P < 0.05) by 73.7% when sulfur was supplemented in FTMR at 2%. The levels of HCN in FTMR were 2.89, 0.61, 0.61 and 0.49 ppm, for ensiling time of 0, 7, 14 and 21 days, respectively (P < 0.01). HCN was reduced when ensiling started at 7 days. Gas production from soluble fractions (a) ranged from –1.2 to –2.4 and was not significant (P > 0.05). Furthermore, gas production from the insoluble fraction (b) ranged from 48.8 to 53.9, and gas production rate constants for the insoluble fraction (c) ranged from 0.1 to 0.2. The potential extent of gas production (a + b) was also unchanged when the concentration of sulfur increased (P > 0.05). In addition, there were no interactions between sulfur levels and ensiling times on all parameters (P > 0.05). In contrast, cumulative gas production (at 96 h of incubation) was significantly different when sulfur increased at 2% (P < 0.05), while ensiling times did not affect cumulative gas production. Ruminal pH was affected by FTMR and decreased with an ensiling time of 21 days, ranging from 6.0 to 6.1 after ensiling. Ensiling time did not affect ruminal ammonia-nitrogen concentration (P > 0.05) among dietary treatments which ranged from 21.2 to 24.0 mg%. FTMR ensiled for 21 days had the highest in in vitro dry matter digestibility, an in vitro neutral detergent fibre and in vitro acid detergent fibre digestibility which were 61.0–62.5, 35.1–43.1 and 22.3–25.9% dry matter (DM) respectively. Regarding the concentration of total volatile fatty acid (VFA), acetic acid, propionic acid and butyric acid, ranges from 94.7 to 113.6 mmol/L, 59.3 to 67.4, 20.2 to 25.9 and 11.3 to 13.8 mol/100 mol, respectively, were observed and did not differ among treatments (P > 0.05). The concentration of total VFA relative to the sulfur level and ensiling time had no effect on ruminal VFA concentrations. However, exceedingly high percentages of sulfur (2% of the DM) in the diet tend to increase total VFA concentration. Conclusions Using of 2% sulfur supplementation in TMR containing fresh cassava root fermented could improve the kinetics of gas and nutrient digestibility while maintaining ruminal fermentation parameters and the rate of HCN disappearance. Implications These findings should be examined in further in vivo experiments in order to increase animal performance.

2020 ◽  
Vol 60 (5) ◽  
pp. 659 ◽  
Author(s):  
Gamonmas Dagaew ◽  
Anusorn Cherdthong ◽  
Metha Wanapat ◽  
Pin Chanjula

Context Feeding ruminants with fresh cassava roots (FCR) is limited because they have a high concentration of hydrocyanic acid (HCN). Thus, it was hypothesised that receiving a feed block containing high sulfur (FBS) would reduce hydrocyanic acid (HCN) in FCR and improve rumen fermentation and nutrient digestibility in animals. Aims The goal of the present work was to study the influence of the ratio of FCR to rice straw (RS) together with FBS on kinetics of gas production, HCN concentration, fermentation characteristics and nutrient digestibility, using in vitro technique. Methods The experimental design was a 4 × 2 factorial arrangement in a completely randomised design, with three replications per treatment. Factor A was the FCR to RS ratio, which was 100:0, 60:40, 40:60 or 0:100. Factor B was sulfur, which was provided as two concentrations in FBS (2% and 4% DM). Gas production was recorded after incubation, at 0, 0.5, 1, 2, 4, 6, 8, 12, 18, 24, 48, 72 and 96 h. Fermentation liquor was collected and determined for kinetics of gas production, HCN concentration, fermentation characteristics and nutrient digestibility. Key results Cassava root to RS ratio influenced the cumulative gas production after 96 h. Inclusion of sulfur in the FBS at 4% increased the cumulative gas production, when compared with inclusion at 2%. The gas production from degradable fraction (b) and the rate of gas production (c) were significantly different among the treatments with different FCR:RS ratios, whereas there was no difference between using 2% and 4% sulfur in the FBS. The HCN concentration in fermentation liquor increased with an increasing proportion of FCR. Furthermore, inclusion of sulfur in the feed block at 4% reduced HCN concentration by 42.8%, when compared with inclusion at 2% (P < 0.05). Ammonia-nitrogen concentration was significantly different among the FCR:RS-ratio treatments and was reduced when the proportion of FCR was decreased (P < 0.05). In vitro digestibility was significantly increased with an increasing proportion of FCR. Increasing the proportion of FCR with 4% of sulfur in the FBS significantly increased in vitro DM digestibility, compared with 2% sulfur. Increasing the FCR:RS ratio with 4% of sulfur in the FBS increased the proportion of propionic acid (P < 0.05). Conclusions Using a high FCR:RS ratio (100:0 or 60:40) with 4% sulfur in the FBS enhanced kinetics of gas production, propionic molar proportion, nutrient digestibility, and HCN detoxification by rumen microbes in an in vitro trial. Implications An in vivo study should be encouraged to verify the results and obtain more data.


Fermentation ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 207
Author(s):  
Chanadol Supapong ◽  
Anusorn Cherdthong

The use of cyanide-containing feed (HCN) is restricted because it causes prussic acid poisoning in animals. The objective of this study was to see how adding rhodanese enzyme to an HCN-containing diet affected gas dynamics, in vitro ruminal fermentation, HCN concentration reduction, and nutrient digestibility. A 3×4 factorial arrangement in a completely randomized design was used for the experiment. Factor A was the three levels of potassium cyanide (KCN) at 300, 450, and 600 ppm. Factor B was the four doses of rhodanese enzyme at 0, 0.65, 1, and 1.35 mg/104 ppm KCN, respectively. At 96 h of incubation, gas production from an insoluble fraction (b), potential extent (omit gas) (a + b), and cumulative gas were similar between KCN additions of 300 to 450 ppm (p > 0.05), whereas increasing KCN to 600 ppm significantly decreased those kinetics of gas (p < 0.05). Supplementation of rhodanese enzymes at 1.0 to 1.35 mg/104 ppm KCN enhanced cumulative gas when compared to the control group (p < 0.05). Increasing the dose of rhodanese up to 1.0 mg/104 ppm KCN significantly increased the rate of ruminal HCN degradation efficiency (DE) by 70% (p < 0.05). However, no further between the two factors was detected on ruminal fermentation and in vitro digestibility (p > 0.05). The concentration of ammonia-nitrogen (NH3-N) increased with increasing doses of KCN (p < 0.05), but remained unchanged with varying levels of rhodanese enzymes (p > 0.05). The in vitro dry matter digestibility (IVDMD) was suppressed when increasing doses of KCH were administered at 600 ppm, whereas supplementation of rhodanese enzymes at 1.0–1.35 mg/104 ppm KCN enhanced IVDMD (p < 0.05). Increasing doses of KCN affected reduced total volatile fatty acids (TVFA) concentration, which was lowest when 600 ppm was added (p < 0.05). Nevertheless, the concentration of TVFAs increased when rhodanese enzymes were included by 1.0–1.35 mg/104 ppm KCN (p < 0.05). Based on this study, it could be concluded that supplementation of rhodaneses enzyme at 1.0–1.35 mg/104 ppm KCN could enhance cumulative gas, digestibility, and TVAF, as well as lowering ruminal HCN concentration.


Author(s):  
Rittikeard Prachumchai ◽  
Anusorn Cherdthong ◽  
Metha Wanapat

The current work aimed to screen the ruminal cyanide-utilizing bacteria and evaluate the influence of fresh cassava root (FCR) and pellets containing high sulfur (PELFUR) on cyanide content, kinetics of gas, in vitro degradability, and ruminal fermentation. The experiment was conducted in a Completely randomized design (CRD) for a screening of cyanide-utilizing bacteria and the dietary treatments were the level of cyanide at 0, 150, 300, and 450 ppm. A 5 &times; 3 factorial arrangement in a Completely randomized design was used for in vitro study. Factor A was the level of FCR at 0, 260, 350, 440, and 530 g/kg of 0.5 g dry matter (DM) substrate, and factor B was the level of PELFUR at 0, 15, and 30 g/kg DM substrate. Adding different doses of cyanide significantly affected cyanide-utilizing rumen bacterial growth (p &lt; 0.05). Increasing the concentration of cyanide from 0 to 150 and 150 to 300 ppm, resulted in an increase in cyanide-utilizing rumen bacteria of 38.2% and 15.0%, respectively. Increasing the FCR level to more than 260 g/kg of 0.5 g substrate could increase cumulative gas production (p &lt; 0.05), whereas increasing doses of PELFUR from 15 to 30 g/kg increased the cumulative gas production when compared with that of 0 g/kg PELFUR (p &lt; 0.05). Cyanide concentration in rumen fluid decreased with PELFUR (p &lt; 0.05) supplementation. Degradability of in vitro dry matter and organic matter following incubation increased at 12 and 24 h due to PELFUR supplementation with FCR and increased additionally with 15 g/kg PELFUR (p &lt; 0.05) in 440 g/kg FCR. Proportions of the total volatile fatty acids, acetic acid (C2), propionic acid (C3), and butyric acid, as well as the ratio of C2 to C3 among supplementations with FCR (p &lt; 0.05) were significantly different. As the proportion of FCR increased to 530 g/kg of the substrate, the volume of C3 increased by 14.6%. This is the first finding of bacteria in the rumen capable of utilizing cyanide, and cyanide might function as a nitrogen source for bacterial cell synthesis. Inclusion of FCR of 530 g/kg with 30 g/kg PELFUR could increase the cumulative gas production, the bacterial population, the in vitro degradability, the proportion of C3, and the rate of the disappearance of cyanide.


2021 ◽  
Vol 34 (1) ◽  
pp. 56-65
Author(s):  
Jiang Chun Wan ◽  
Kai Yun Xie ◽  
Yu Xiang Wang ◽  
Li Liu ◽  
Zhu Yu ◽  
...  

Objective: This study was conducted to investigate the effects of molasses and <i>Lactobacillus plantarum</i> on the ensiling quality and <i>in vitro</i> rumen fermentation of sudangrass silage prepared with or without wilting.Methods: The ensiling experiment, measured with 3 replicates, was carried out according to a 2×4 (wilted stages×additives) factorial treatment structure. Dry matter of the fresh (210 g/kg fresh matter) or wilted (305 g/kg fresh matter) sudangrass were ensiled (packed into 5.0-L plastic jars) without additive (control) or with molasses (M), <i>Lactobacillus plantarum</i> (LP), or molasses + <i>Lactobacillus plantarum</i> (M+LP). After 60 days of ensiling, the silages were analyzed for the chemical, fermentation, and <i>in vitro</i> characteristics.Results: After 60 days of ensiling, the fermentation parameters were affected by wilted, the additives and the interactions of wilted with the additives (p<0.05). The M+LP treatment at wilted had higher lactic acid levels and V-score (p<0.05) but lower pH values and butyric acid concentrations than the other treatments. In comparison with sudangrass before ensiling, after ensiling had lower dry matter and higher non-fibrous carbohydrate. The <i>in vitro</i> gas production, <i>in vitro</i> dry matter digestibility, <i>in vitro</i> crude protein digestibility, and <i>in vitro</i> acid fiber detergent digestibility changed under the effects of the additives. Significant interactions were observed between wilted and the additives in terms of <i>in vitro</i> gas production at 48 h, asymptotic gas production, gas production rate, half time, and the average gas production rate. The total volatile fatty acid levels in the additive treatments were higher than those in the control.Conclusion: Wilting and supplementation with molasses and <i>Lactobacillus plantarum</i> had the ability to improve the ensiling quality and <i>in vitro</i> nutrient digestibility of sudangrass silage. The M+LP treatment at wilted exhibited the strongest positive effects on silage quality and <i>in vitro</i> ruminal fermentation characteristics.


2019 ◽  
Vol 97 (7) ◽  
pp. 3089-3102 ◽  
Author(s):  
Lucas B Kondratovich ◽  
Jhones O Sarturi ◽  
Carly A Hoffmann ◽  
Michael A Ballou ◽  
Sara J Trojan ◽  
...  

Abstract The effects of dietary pretreatment with fibrolytic enzyme-based cocktail were evaluated in 2 studies: (1) in vitro true digestibility; and (2) intake, digestibility, feeding behavior, and ruminal fermentation of beef steers fed growing diets. For the in vitro assessment, the ruminal inoculum was collected from 2 steers (BW = 543 ± 45 kg; 4-h after feeding; growing diets) and enzymes included or not (Trichoderma reesei fermentation extract; 0.75 µL/g of substrate DM). Within in vitro batches (n = 4), 12 substrates were incubated and in vitro true nutrient digestibility was evaluated. For study 2, 5 ruminally cannulated beef steers (BW = 520 ± 30 kg) were used in a 5 × 4 unbalanced Latin square using a 2 × 2 factorial arrangement of treatments: (a) diet quality (high = HQ; and low = LQ) and (b) enzyme inclusion (0 or 0.75 mL/kg of diet DM). Steers were fed ad libitum during four 21-d periods consisting of 14-d of adaptation and 7-d of collections. An enzyme × substrate was observed (P < 0.01), in which DM, OM, and NDF disappearance of sorghum grain increased with enzymes addition. Addition of enzymes increased (P < 0.01) ADF digestibility for all substrates. No diet quality × enzyme (P ≥ 0.18) was observed for intake variables in study 2. Enzyme-fed steers increased (P ≤ 0.05) intake of DM, digestible DM, NDF, and ADF compared with steers not fed fibrolytic enzymes. Addition of enzyme did not affect (P ≥ 0.28) apparent total tract digestibility of beef steers. Steers fed HQ diets consumed more (P ≤ 0.04) DM, digestible DM and OM, and less (P ≤ 0.03) total and digestible fiber than steers fed LQ diets. Ruminal pH average decreased (P = 0.01) for steers fed HQ or enzyme-fed diets compared with other treatments. A tendency (P = 0.06) toward improved total VFA was observed on enzyme-fed steers with HQ diets, but not for LQ diets. The molar proportion of ruminal propionate increased (P = 0.01) when steers were fed enzyme. Steers fed HQ diets had greater (P < 0.01) propionate and valerate molar proportions, lower (P < 0.01) acetate and acetate:propionate ratio than steers fed LQ diets. In vitro methane and total gas production were not affected (P ≥ 0.50) by dietary treatments. Fibrolytic enzymes positively affected digestion of multiple roughage sources commonly fed to cattle and might have additional benefit when used on unprocessed sorghum grain. Fibrolytic enzymes in beef cattle growing diets stimulated intake and generated positive impacts on ruminal fermentation.


Author(s):  
Phussorn Sumadong ◽  
Anusorn Cherdthong ◽  
Sarong So

The study aimed to elucidate the optimum level of elemental sulfur, fresh cassava root (FCR), and urea and their effect on gas production, ruminal fermentation, thiocyanate concentration, and in vitro degradability. A 3&times;2&times;4 in a completely randomized design were conducted. Factor A was level of sulfur at 0%, 1%, and 2% of concentrate dry matter (DM), factor B was level of urea at 2% and 4% of concentrate DM, and factor C was level of the FCR at 0, 200, 300, and 400 mg of the total substrate. The study found that elemental sulfur, urea, and FCR had no interaction effect on the kinetics of gas, ruminal fermentation, hydrogen cyanide (HCN), and in vitro degradability. Elemental sulfur supplementation (P&lt;0.05) significantly increased the gas produced from an insoluble fraction (b), in vitro DM degradability and either neutral detergent fiber or acid detergent fiber degradability, and propionate (C3) concentration while decreased the ruminal HCN concentration. Urea levels showed a (P&lt;0.05) significant increase of the potential extent of gas production, ruminal NH3-N, and total volatile fatty acid (VFA). FCR supplementation (P&lt;0.05) significantly increased the gas produced from an immediate soluble fraction (a), gas produced from insoluble fraction, gas production rate constant, total VFA, C3 concentration, and HCN while decreased ruminal pH, acetate, and butyrate concentration. It could be concluded that 2% elemental sulfur, 4% urea, and 300 mg FCR showed a greater effect on gas production, ruminal fermentation, and HCN reduction.


2021 ◽  
Author(s):  
Phussorn Sumadong ◽  
Anusorn Cherdthong ◽  
Sarong So ◽  
Metha Wanapat

Abstract Background: Cassava root (FCR) is one of the main energy source ingredients for ruminant and low price. The limitation of FCR utilization is due to the presence of hydrogen cyanide (HCN), which is toxic when animals, especially ruminants. The study aimed to evaluate the effect of sulfur, urea, and FCR at various levels on gas production, ruminal fermentation, and in vitro degradability. The study hypothesized that: 1) sulfur, urea, and FCR have no interaction effect and 2) effect of FCR and urea is related to sulfur addition. Results: The study aimed to elucidate the optimum level of elemental sulfur, fresh cassava root (FCR), and urea and their effect on gas production, ruminal fermentation, thiocyanate concentration, and in vitro degradability. A 3×2×4 in a completely randomized design were conducted. Factor A was level of sulfur at 0%, 1%, and 2% of concentrate dry matter (DM), factor B was level of urea at 2% and 4% of concentrate DM, and factor C was level of the FCR at 0, 200, 300, and 400 mg of the total substrate. The study found that elemental sulfur, urea, and FCR had no interaction effect on the kinetics of gas, ruminal fermentation, hydrogen cyanide (HCN), and in vitro degradability. Elemental sulfur supplementation (P<0.05) significantly increased the gas produced from an insoluble fraction (b), in vitro DM degradability and either neutral detergent fiber or acid detergent fiber degradability, and propionate (C3) concentration while decreased the ruminal HCN concentration. Urea levels showed a (P<0.05) significant increase of the potential extent of gas production, ruminal NH3-N, and total volatile fatty acid (VFA). FCR supplementation (P<0.05) significantly increased the gas produced from an immediate soluble fraction (a), gas produced from insoluble fraction, gas production rate constant, total VFA, C3 concentration, and HCN while decreased ruminal pH, acetate, and butyrate concentration. It could be concluded that 2% elemental sulfur, 4% urea, and 300 mg FCR showed a greater effect on gas production, ruminal fermentation, and HCN reduction.Conclusions: The study found that elemental sulfur, urea, and FCR had no interaction effect on the kinetics of gas, total gas, ruminal fermentation, and HCN concentration. It could be concluded that 2% elemental sulfur, 4% urea, and 300 mg FCR showed a greater effect on gas production, ruminal fermentation, and HCN reduction.


2021 ◽  
Vol 17 (1) ◽  
Author(s):  
Phussorn Sumadong ◽  
Anusorn Cherdthong ◽  
Sarong So ◽  
Metha Wanapat

Abstract Background Total fresh cassava root (FCR) production was 275 million tonnes in 2018 which equals 61.1 % of the total production, and Thailand produced 10.7 % FCR of the total production. FCR is one of the main energy source for ruminant. The limitation of FCR utilization is due to the presence of hydrogen cyanide (HCN). The study aimed to evaluate the effect of sulfur, urea and FCR at various levels on in vitro gas production, ruminal fermentation and in vitro degradability. The study hypothesized that: (1) sulfur, urea and FCR have no interaction effect and (2) effect of FCR and urea is related to sulfur addition. Results The study aimed to elucidate the optimum level of elemental sulfur, fresh cassava root (FCR) and urea and their effect on in vitro gas production, ruminal fermentation, thiocyanate concentration, and in vitro degradability. A 3 × 2 × 4 in a completely randomized design were conducted. Factor A was level of sulfur at 0 %, 1 and 2 % of concentrate dry matter (DM), factor B was level of urea at 2 and 4 % of concentrate DM, and factor C was level of the FCR at 0, 200, 300 and 400 mg DM of the total substrate. The study found that elemental sulfur, urea and FCR had no interaction effect on the kinetics of in vitro gas, ruminal fermentation, HCN and in vitro degradability. Elemental sulfur supplementation (P < 0.05) significantly increased the in vitro gas produced from an insoluble fraction (b), in vitro DM degradability and either neutral detergent fiber (NDF) or acid detergent fiber (ADF) degradability and propionate (C3) concentration while decreased the ruminal HCN concentration. Urea levels showed a (P < 0.05) significant increase of the potential extent of in vitro gas production, ruminal ammonia nitrogen (NH3-N) and total volatile fatty acid (TVFA). Fresh cassava root supplementation (P < 0.05) significantly increased the in vitro gas produced from an immediate soluble fraction (a), in vitro gas produced from insoluble fraction, in vitro gas production rate constant, total VFA, C3 concentration and HCN while decreased ruminal pH, acetate and butyrate concentration. It could be concluded that 2 % elemental sulfur, 4 % urea and 300 mg FCR showed a greater effect on in vitro gas production, ruminal fermentation and HCN reduction. Conclusions The study found that elemental sulfur, urea, and FCR had no interaction effect on the kinetics of in vitro gas, total in vitro gas, ruminal fermentation, and HCN concentration. It could be concluded that 2 % elemental sulfur, 4 % urea, and 300 mg FCR showed a greater effect on in vitro gas production, ruminal fermentation, and HCN reduction.


Agriculture ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1205
Author(s):  
Musen Wang ◽  
Fujin Zhang ◽  
Xinxin Zhang ◽  
Ying Yun ◽  
Lei Wang ◽  
...  

The objective of this work was to evaluate the pH, chemical composition, minerals, vitamins, and in vitro rumen fermentation characteristics of silage prepared with lucerne, sweet maize stalk (MS), and their mixtures. Freshly chopped lucerne and MS were combined in ratios of 100:0 (M0, control), 80:20 (M20), 60:40 (M40), 40:60 (M60), 20:80 (M80), and 0:100 (M100) on a fresh matter basis. Each treatment was prepared in triplicate, and a total of eighteen silos were fermented for 65 days. After 65 days of fermentation, the pH values in M0, M20, M40, M60, M80, and M100 silages were 5.47, 4.84, 4.23, 4.13, 3.79, and 3.61, respectively. As the MS proportion in the mixtures increased, silage K, Ca, P, Na, Fe, and Cu concentrations linearly decreased (p < 0.001) and so did vitamins B5 and K1 and α-tocopherol. In vitro rumen dry matter and organic matter degradability, pH, ammonia, total volatile fatty acid, and gas production linearly decreased (p < 0.01), while neutral detergent fiber concentration linearly increased (p < 0.001), with increasing proportion of MS. The in vitro dry matter and organic matter degradability rapidly decreased when the MS percentage was ≥60%. In conclusion, the M40 silage is the most suitable for livestock utilization in local forage production considering the balance of silage pH, nutritional quality, and in vitro ruminal fermentation characteristics.


2016 ◽  
Vol 16 (2) ◽  
pp. 333-341
Author(s):  
Seyed Masoud Davoodi ◽  
Mohsen Danesh Mesgaran ◽  
Ali Reza Vakili ◽  
Reza Valizadeh ◽  
Abdollah Ghasemi Pirbalouti

Present study was conducted to investigate the effect of including plant essential oils on in vitro ruminal fermentation and microbial nitrogen synthesis of a dairy cow diet rich in concentrate. The treatments consisted of the diet alone (control; BD) as well as containing 50 and 100 μl L-1 essential oil of thyme (BDT), mint (BDM), savory (BDS), or a mixture of the essential oils at the rate of 1:1:1 (BDmix). Essential oils decreased gas production at 24, 48 and 96 h of incubation compared with that of BD. However, mint at the rate of 50 or 100 μl L-1 resulted an increase in the microbial nitrogen when compared to BD, BDS and BDT. The nitrogen content of truly undegraded residu (NDFN) content and NH3-N concentration were lower, while the dry matter digestibility was greater in the BDmix, regardless of dosage levels, as compared with the control. The inclusion of a mixture of essential oils at 50 μl L-1 to the basal diet caused intensified dry matter disappearance, in comparison to other treatments. Results showed that the synergetic effects of essential oils together in a dairy cow diet of rich in concentrate can alter rumen microbial fermentation and improve microbial protein yield.


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