Fermentation losses and chemical composition of Calotropis procera ensiling with mango and tomato waste

R F Santos, J L Silva, A A C Ferreira, M S Mello, M A Ferreira¹, M C B Siqueira¹, J G Inácio¹ and A J B Pimentel

Universidade Federal do Oeste da Bahia, 23 August Avenue, Assunção, Barra, Brazil
silva.janainalima@gmail.com
¹ Animal Science Department, Universidade Federal Rural de Pernambuco, Dom Manoel de Medeiros Street, Dois Irmãos, Recife, Brazil

Abstract

The objective of this work was to evaluate fermentative losses, chemical composition and sensorial quality of silk flower ensiling with four levels of mango and tomato waste (0.00, 10.0, 15.0 and 20.0% of fresh matter). The material was ensiled for 60 days in polyvinyl chloride (PVC) silos. There was a maximum production of effluent (22.1 kg/ton of fresh matter) by including 12.3% of mango and tomato waste (p <0.05). The maximum recovery of dry matter (95.3%) was obtained by including 9.38% of mango and tomato waste (p <0.05). The maximum point of 17.2% of dry matter and 65.1% of non-fibrous carbohydrates was observed by including 13.5% and 12.9% of mango and tomato waste (p <0.05). In the sensorial evaluation, a “good to very good” classification was recorded when 10.0, 15.0 and 20.0% of fresh matter of mango and tomato waste were included. In conclusion, the inclusion of 13.0% of mango and tomato waste is recommended for silk flower silage because of adequate contents of dry matter, crude protein, and non-fibrous carbohydrates associated to lower fermentative losses when compared to the control silage.

Keywords: effluent, ensiling, non-fibrous carbohydrates, sensorial analysis, silk flower

Introduction

The Brazilian semiarid occupies about 70.0% of the Brazilian territory. It covers the states of the Northeast and North of Minas Gerais and a great territorial extension in the state of Bahia. The region is characterized by a dry and hot climate, with predominant Caatinga vegetation, and low rainfalls (IBGE 1998). Rainfall is the main limitation factor for animal production in the Brazilian semiarid region. It causes low forage production during the dry period. According to IBGE, the northeast region lost 4 million animals in 2012, with a marked reduction of 4.50% in the cattle herd compared to 2011.

Thus, in order to maintain the sustainability of animal production in the semiarid region, farmers should not depend on the use of native or cultivated pastures. It is necessary to conserve forage (hay or silage) to supply the demand by animals for food. In addition, it is imperative to conduct studies that make feasible the use of alternative food in animal supplementation, such as plants of natural occurrence and adapted to the region, or byproducts of food processing and post-harvest waste.

There are few researches on native or introduced plants with the potential for feeding ruminants, such as silk flower (also called silk cotton) (Calotropis procera) (Madruga et al 2008), which belongs to the family Apocynaceae. Some studies have shown that this species has a high protein content and a high dry matter digestibility (DM). It can be supplied as silage or hay for ruminant feeding (Belém et al 2006; Madruga et al 2008). Silk flower is a native plant of Africa, but can be found in several locations in Brazil. It is an invasive plant difficult to eliminate (Leal et al 2013). The main attributes of silk flower are resistance to water deficit, vigorous regrowth after cutting, and good development in saline soils (Frosi et al 2013; Ibrahim 2013). On the other hand, it presents a low palatability when offered in natura and is toxic to some extent (Lima et al 2011). The literature contains few studies on the conservation strategies of silk flower and its nutritional value, mainly when used as silage.

In addition to naturally occurring plants and plants adapted to the semiarid region, waste from the production of fruits and vegetables can be alternative ingredients for ruminant feeding, mainly small ruminants, during forage shortage periods. According to Vidal & Ximenes (2016), fruit growing is one of the most prominent segments of agriculture mainly in the Western Bahia. Bahia is the largest producer of banana, coconut, orange, papaya, mango, passion fruit, and watermelon. The production of such fruits and vegetables in Brazil is associated with annual increases in postharvest losses in fields, supermarkets, and consumer residences (Fehr and Romão 2001). The fruits could be conserved as silage for later use for the diet of ruminants.

According to McDonald et al (1991), the production of a good silage depends on proper amounts of soluble carbohydrates (6.00-8.00% in DM) and dry matter (content above 30.0%). Tropical forage plants are known for the low DM and soluble carbohydrates content. It is necessary to proceed with plant wilting, increasing of moisture due to absorbing of additives, or addition of soluble carbohydrates in order to allow a good fermentability of the silage. Wadhwa and Bakshi (2013) reported that peels and waste of mango, banana, citrus, pineapple, tomato, among others, can be ensiled and supplied to ruminants.

Therefore, considering forage scarcity for animal feeding in drought periods in the Brazilian semiarid region, the widespread occurrence of silk flower, and the high availability of fruit and vegetable waste, the aim of this study was to evaluate fermentative losses, chemical composition, and sensory quality of silk flower ensiled with different levels of mango and tomato waste.

Material and Methods

The study was conducted at the Barra Campus of the Universidade Federal do Oeste da Bahia (UFOB), located in Barra, Brazil, from September to November 2017, at 11°05'20" S and 43°08'31" W, and altitude of 406 m. The treatments consisted of different levels of inclusion of mango and tomato waste in silk flower silage: 0.00, 10.0, 15.0 and 20.0% of fresh matter (FM). In each treatment, the FM of mango and tomato waste was equally added.

Mango (peels and pulp) and tomato (peels, pulp, and seeds) waste were obtained in local markets and in rural properties of Barra, Bahia. The material (mango and tomato) was ground by hand to obtain a 2-cm particle size, and placed on plastic canvas under the sun for dehydration for 10 hours, reaching a DM content of 37.9%. The leaves of silk flower were collected in vacant lots and roadsides (Photo 1). Then, they were crushed in a forage machine, obtaining particles of 2 cm, and subsequently wrapped in plastic canvas and placed under the sun for 8 hours, reaching a DM content of 15.4%. After this period, the additives (mango and tomato waste) were added to the wilted silk flowers, according to the proposed treatments, and immediately ensiled. Samples of wilted silk flowers and mango and tomato waste were collected and stored as original material for further DM analysis.

Photo 1. Silk flower (Calotropis procera) in vacant lot before the collect

The experimental unit consisted of an experimental silo made of polyvinyl chloride (PVC), 50 cm high and 10 cm in diameter. The bins of the silos were equipped with Bunsen valves to allow the quantification of gases obtained by fermentation. At the bottom of each silo, 1.00 kg of sand was placed, separated from the forage by a cotton cloth, in order to capture the effluent from the forage silage. The compaction of the material was performed manually by using wooden sockets. The compacted material was subsequently sealed with plastic film and PVC lids, and then rested for 60 days. Four replicates were adopted for each treatment. The experiment was completely randomized.

The density of silages was calculated by the ratio between ensiled forage mass and silo volume. The empty set (silo, lid, plastic film, sand, and cotton cloth) was weighed to quantify effluent production, gas loss, total DM loss, and DM recovery using the equations proposed by Jobim et al (2007). Samples of in natura silages were manually pressed and filtered with filter paper to extract the silage broth, which was used immediately to determine the pH using a potentiometer.

The silages were analyzed for the determination of DM (INCT-CA G-003/1), organic matter (OM), mineral matter (MM; INCT-CA N-001/1), total nitrogen (N; INCT-CA N-001/1), ether extract (EE; INCT-CA G-004/1), neutral detergent fiber (NDF; INCT-CA F-002/1), and acid detergent fiber (ADF; INCT-CA F-004/1) according to methodologies described by Detmann et al (2012). Non-fibrous carbohydrates (NFC) were estimated using the equation recommended by Hall et al (1999): %NFC = 100 - (%CP + %EE + %NDFap + %MM), where NDFap is the neutral detergent fiber corrected for ash and protein, and CP is crude protein (%CP = %N x 6.25).

For the sensory evaluation of silages, thirty evaluators (men and women randomly selected) were trained on the scoring of the evaluation form. At the moment of opening of the silos, the sensory evaluation of silages was carried out according to the criteria established by Meyer et al (1989): (i) odor, (ii) color, iii) texture, and iv) contamination (sanitary aspects evaluated only by odor). The quantification and identification of microorganisms, or microbiological analyses were not the object of the present study. The silages received scores for each of the aspects mentioned. The sum of scores were classified as good to very good, satisfactory, regular, and unsatisfactory.

The data were analyzed by analysis of variance and regression using the System of Statistical Analysis of the SAEG software (version 9.1), adopting a level of significance of 5.00% for type I error. The Dunnett test was used to compare the control treatment (silk flower silage without the addition of mango and tomato waste) with the other treatments (levels of inclusion of mango and tomato waste).

Results and Discussion

There were no effects for the inclusion levels of mango and tomato waste on density, gas losses, and pH of silk flower silages. The mean values were 588 kg FM/m³, 4.91% and 3.39, respectively. However, by Dunnett test, treatments with mango and tomato waste showed lower gas losses and pH values when compared to the control silage (Table 1). The density obtained for silk flower silage, with or without mango and tomato waste, presented an adequate value, corroborating Ruppel et al (1995), who recommended densities higher than 550 kg FM/m³ and lower than 850 kg FM/m³ as ideal for the conservation of forage as silage. Belém et al (2016) found no effects of the addition of grape waste on the density of silk flower silage. The mean value was 486 kg FM/m³, lower than that observed in the present study and below the value considered ideal.

One way of evaluating the quality of silage fodder fermentation is to measure gas losses, effluents, and total DM in silage using laboratory silos (PVC silos or plastic buckets) containing a suitable lid (Bunsen valve) to analyze the elimination of gases, and sand to analyze effluent recovery (Jobim et al 2007). According to McDonald et al (1991), when low density silages are produced, the probability of containing more residual air in the ensiled mass is increased. Consequently, there are a higher loss by respiration (CO₂  release and loss of DM), lower aerobic stability, and higher post-opening losses, which leads to an increase in the final pH and silage DM losses. In the present study, there was a positive effect of the addition of mango and tomato waste due to an adequate compaction of silages and adequate densities, providing fermentative stability of the ensiled mass, which presented lower gas losses and a lower pH compared to the control silage.

The pH evaluated in silages with a low DM content is a good indicator of the quality of the final product (Jobim et al 2007), that is, forage ensiling with a low moisture (excess of wilting) tends to present pH values above 4.20, which are considered of poor quality. According to McDonald et al (1991), the pH considered ideal ranges from 3.50 to 4.20. In this study, silk flower silage without additive presented a value within this range, and the other treatments presented slightly lower values.

The effluent loss was higher in the silage with the inclusion of 10.0% of mango and tomato waste when compared to the control silage (Table 1). There was a quadratic behavior for this variable, with a maximum effluent loss of 22.1 kg/ton of FM due to the inclusion of 12.3% of mango and tomato waste in silk flower silage. The result found in this study is higher than the result verified by Belém et al (2016): 1.69 kg/ton of FM using 10.6% of grape waste. This result occurs because this additive has a higher DM content than mango and tomato waste. According to Balieiro Neto et al (2009), during the silage process, the higher the moisture content of the silage forage, the greater the loss of effluents, which explains the higher effluent production of up to 12.3% of the mango and tomato waste used in the present study.

For total DM loss and DM recovery, all inclusion levels of mango and tomato waste differed from the control silage (Table 1). In addition, a quadratic behavior was observed for both variables. The minimum total loss of DM was 4.66%, and the consequent maximum recovery of DM was 95.3% with the inclusion of 9.38% of mango and tomato waste. These results were slightly lower than those reported by Belém et al (2006): total DM loss of 1.38% and DM recovery of 98.6%. However, the results obtained in the present study indicate an adequate preservation of silage with the addition of mango and tomato waste up to 9.38%. This value can be explained by the quadratic behavior of DM, which increased up to 16.6% of waste addition.

DM, OM and NFC contents of silk flower silages, with the inclusion of 10.0, 15.0 and 20.0% of mango and tomato waste, differed and were higher than the control silage (Table 2). This fact can be explained by the process of dehydration of the additives, which increased the initial content of DM and consequently of OM during ensiling. There was a quadratic behavior for DM content. The maximum point was 17.2% with the inclusion of 13.5% of mango and tomato waste. The DM levels verified in the present study are lower than the values reported by Belém et al (2016): maximum value of 29.0% with 40.0% inclusion of grape waste. Grape waste has a higher DM content (50.7%) at the time of ensiling.

OM and NFC contents presented the same quadratic behavior as the DM, but with a maximum point of 82.5% OM and 65.1% NFC with the inclusion of 9.12% and 12.9% of mango and tomato waste, respectively. This result is close to the OM content (87.6%) reported by Lima et al (2005). The authors evaluated silk flower silage with 12 hours of pre-drying. In addition, the value is similar to the OM content of in natura silk flower (86.7%) harvested 60 days after regrowth, as reported by Andrade et al (2008). There are little changes during the fermentation process in the silo. However, the NFC content of silk flower silages with 12.9% of mango and tomato waste is higher than the content reported by Andrade et al (2008), i.e., 25.2% in fresh forage. This fact evidences an improvement in nutritional value by the addition of mango and tomato waste. Aragão et al (2012), evaluating different parts of mango, found average values of NFC of 59.6% in peels and 69.3% in the pulp. For the in natura tomato bagasse, Pimentel et al (2017) reported 17.2%, which justifies the increase in the NFC content of the silages evaluated in the present study.

The inclusion levels of 10.0, 15.0 and 20.0% of mango and tomato waste to silk flower provided different (p <0.05) and lower levels of CP, EE, NDF, ADF, and MM when compared to the control silage (Table 2). There was a linear reduction of 0.27% in CP content and 0.24% in EE content for each 1.00% increase in mango and tomato waste. These values could be explained by the quadratic behavior of OM content, which decreased when the addition of mango and tomato waste was higher than 9.12%.

The reduction observed in CP levels in silk flower silages as the level of additives increased, compared to the control silage, could be explained by the low protein levels in mango and tomato waste. Aragão et al (2012), evaluating different parts of mango, found average CP values of 3.90% in peels and 3.40% in the pulp. In a byproduct of tomato, Ventura et al (2009) verified about 17.0% of CP. The levels of CP verified in the literature only for silk flower vary from 15.0 to 20.0%. Fall Touré et al (1998) reported 15.9% of CP in leaves pre-dried under the sun. Andrade et al (2008) reported 19.4% of CP in fresh silk flowers, which explains the reduction in protein contents in the silages in the present study, in which the silk flower was partially replaced by mango and tomato waste.

According to Sampaio et al (2009), among the nutrients contained in ruminant diets, protein is the most limited nutrient. It is found at concentrations below 7.00% in most tropical forages. According to Van Soest (1994), this level is lower than the nitrogen content required by ruminal bacteria. Although the silage additives containing mango and tomato waste showed a reduced protein content compared to the control silage, they were higher than the minimum recommended by Van Soest (1994). It also surpasses the protein content by 12.9%, as obtained by Torres et al. (2010) in the evaluation of silk flower hay, and 10.7% as obtained by Lima et al (2005) in the evaluation of silage of silk flowers pre-dried for 12 hours. In addition, silk flower silage can be considered an important alternative food resource for semiarid regions since its protein content surpasses the contents of traditional silages, such as sugarcane additive with Lactobacillus buchneri (3.34%), as observed by Balieiro Neto et al (2009).

The addition of mango and tomato waste in silk flower silages also promoted a quadratic effect on fibrous carbohydrate (FC) contents, with minimum contents of 20.0% NDF and 13.6% ADF with the inclusion of 11.6% and 10.9% of waste, respectively (Table 2). The NDF and ADF levels obtained in the present study are lower than the levels verified by Andrade et al (2008) for fresh silk flower (42.2% NDF and 28.4% ADF), and by Lima et al (2005) for silk flower silage with 12 hours of pre-drying (46.3% NDF and 30.1% ADF). The lower contents of fibrous carbohydrates in the silages of this study are due to the addition of mango and tomato waste. Aragão et al (2012), evaluating different parts of mango, found mean NDF values of 39.1% in peels and 22.9% in the pulp. In byproducts of tomato, Ventura et al (2009) verified about 26.0% of NDF.

For ruminants, the National Research Council (NRC, 2001) recommends a minimum of 25.0% NDF in the dietary DM, and at least 75.0% of that NDF should come from long forage or coarsely chopped forage; in other words, the silages evaluated in the present study could serve as roughage in the proportion of total diet of dairy or beef cattle.

In the sensory evaluation of the characteristics associated to nutritive value, a "satisfactory" classification was obtained for the control silage, and a "good to very good" classification was obtained when mango and tomato waste was added at 10.0, 15.0 and 20.0% (Table 3). Most evaluators considered the odor of the silage to be pleasant, the color a typical green, and adequate DM content in the silage manipulation for silage with mango and tomato waste. This result shows that the addition of fruits and vegetables in silk flower silage is a good alternative to improve the fermentative quality of the silage. Such improvement was probably related to the increase in NFC contents, which in turn provides a higher amount of soluble sugars for lactic acid bacteria (LAB).

As for the characteristics associated with sanitary aspects, all evaluators classified the silage as "good to very good", i.e., with a pleasant odor, no fungi, or an adequate consistency (Table 4). This result was probably related to the adequate dry matter content in the silage, to the presence of soluble carbohydrates for lactic acid bacteria, and to the absence of oxygen due to an adequate process of compaction and silage sealing, protecting against undesirable microorganisms.

The evaluation of qualitative attributes of silage (sensory analysis) using scores assigned by evaluators demonstrates a high correlation with the results of quantitative attributes such as pH, chemical composition, and density (Teixeira et al 2017). That is, the silages classified as "good to very good" in the present study presented an adequate density, pH, and chemical composition. Teixeira et al (2017), evaluating winter grain silages (wheat and oats), and Jian et al (2015), evaluating mixed and wilted mixed silages of oats and alfalfa, reported a high correlation of qualitative (sensory) and quantitative (pH, acid, and fungus concentration) results. This evidences the importance of sensorial attributes (odor, coloration, and texture) for the process of evaluation of silage since such attributes directly interfere with the acceptability of this roughage by animals.

Conclusions

• The recommendation is to include 13% of mango and tomato waste in silk flower silage due to the adequate contents of dry matter, crude protein, and non-fibrous carbohydrates associated to low fermentative losses when compared to the control silage.

Acknowledgments

The authors would like to thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the Scientific Initiation Scholarship granted.

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Received 24 May 2019; Accepted 5 June 2019; Published 2 July 2019

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