ORIGINAL ARTICLE

Physicochemical and biological indicators in silages of taro (Colocasia esculenta (L.) Schott) tubers for animal feeding

Indicadores físico-químicos y biológicos en ensilados de tubérculos de (Colocasia esculenta (L.) Schott) para la alimentación animal

W. Caicedo,^I R. Rodríguez,^II P. Lezcano,^III J. Ly,^III S. Valle,^I L. Flores,^IV F.N.A. Ferreira,^V

ABSTRACT

For assessing the physicochemical and biological indicators in silages of taro (Colocasia esculenta (L.) Schott) tubers for animal feeding, four silages with waste tubers were made.  Treatments were: (1_NY) natural yogurt, (2_W) whey, (3_WMB5) whey and 5 %molasses B and 4_WMB10) whey and 10 % molasses B.  The experimental design was a completely randomized of simple classification. Regarding the temperature at day zero, treatment 2_W showed the highest value (P < 0.05) (22.65 ºC). At day one, 1_NY exhibited the highest value (P < 0.05) (22.53 ºC).  At days two and three in treatment 2_W the highest values were obtained (P < 0.05) (22.53 – 22.49 ºC). From day four, to 180 in the 4_WMB10 the highest temperature was reached 22.83 – 22.54 ºC.  Regarding pH, at day 0, treatment 3_WMB5 presented the highest value (P < 0.05) 5.4.  From day 1 to 4, pH was proportionally reduced in the silages being higher in treatment 2_W, in 0.71 units from day 5 to 180.  Later, the pH was stabilized in all silages.  Treatment 3_WMB5 showed the lowest value (P < 0.05) (3.93 – 3.83).  Fungi, yeasts, total coliform and Escherichia coli were present on day zero and later were absent.  There was no Clostridium spp. or Salmonella spp. throughout the study. The physicochemical and microbiological indicators in the silages until day 180 showed a perfect performance, fit for animal feeding.

Key words: tubers, fermentation, microorganisms, animal feeding.

Con el propósito de evaluar los indicadores físico-químicos y biológicos en ensilados de tubérculos de papa china (Colocasia esculenta (L.) Schott) para su empleo en la alimentación animal, se realizaron cuatro ensilados con tubérculos de desecho. Los tratamientos fueron: (1_YN) yogurt natural, (2_SL) suero de leche, (3_SLMB5) suero de leche y miel B 5 % y (4_SLMB10) suero de leche y miel B 10 %. El experimento se condujo mediante un diseño completamente aleatorizado de clasificación simple. Con respecto a la temperatura, en el día cero, el tratamiento (2_SL) presentó el mayor valor (P < 0.05) (22.65 ºC). En el día uno, el (1_YN) mostró el valor más alto (P < 0.05) (22.53 ºC). En los días dos y tres, en el tratamiento (2_SL) se obtuvieron los mayores valores (P < 0.05) (22.53 - 22.49 ºC). Desde el día cuatro, al 180, en el (4_MB10) se alcanzó la mayor temperatura (22.83 - 22.54 ºC). Con respecto al pH, en el día cero, el tratamiento  (3_MB5) presentó el mayor valor (P < 0.05) 5.4. A partir del día 1 al 4, el pH se redujo proporcionalmente en los ensilados, y fue mayor en  tratamiento (2_SL), en 0.71 unidades del día 5 al 180. Luego, el pH se estabilizó en todos los ensilados. El tratamiento  (3_MB5) mostró el menor valor (P < 0.05) (3.93-3.83). Los hongos, levaduras, coliformes totales y Escherichia coli estuvieron presentes en el día cero, y después se ausentaron. No hubo Clostridium spp. ni Salmonella spp. durante el estudio. Los indicadores físico-químicos y microbiológicos de los ensilajes hasta el día 180 tuvieron un comportamiento idóneo, aptos para su uso en la alimentación animal.

Palabras clave: tubérculos, fermentación, microorganismos, alimentación animal.

INTRODUCTION

Alternative feeds, because of its perishable condition, cannot be stored without processing for preserving its nutritive value.  In addition, since they can be available in large volume only in certain periods, cannot be used completely in animal feeding (Domínguez et al. 2012 and Fránquez et al. 2012).

In Ecuador, there are viable alternative feeds for animal feeding that are not utilized because their nutritional characteristics are not known.  Among these are the taro (Colocasia esculenta (L.) Schott) tubers that contain excellent nutrients for its utilization in the animal diet (Caicedo 2013).  This condition facilitates the possibility of applying the ensiling technique as alternative for preserving these products for a long time and assure animal feeding (Caicedo et al. 2013).

The ensiling technique allows preserving the nutrients in humid stage and limits the development of putrefactive and pathogen microorganisms that provoke great losses of the raw material employed (Balsinde et al. 2003 and Zynudheen and Ramachandran 2008). For obtaining a good quality silage, it is required a fast stabilization of temperature and pH. In this way a final product with optimum microbiological quality is obtained and risks of diseases are prevented in the animals consuming it (Driehuis and Elferink 2000, Posada et al. 2007 and Driehuis 2013).

The objective of this research was to assess the physicochemical and biological indicators in silages of taro (Colocasia esculenta (L.) Schott) tubers for animal feeding.

MATERIALS AND METHODS

The experiment was carried out in the facilities of the agricultural farm “El Progreso” belonging to the parish “Tarqui” located in Pastaza province, Ecuador.  This region has a semi-warm or humid subtropical climate with rainfall ranging between 4000 and 4500 mm annually.  It is located at a height of 900 masl with an average relative humidity of 87 % and an average minimum and maximum temperature of 20 to 28 ºC (INAMI 2013).

For silage preparation (table 1) the recommendations of Caicedo (2013) were followed. Microsilos preparation was carried out with waste tubers which according to its appearance do not fulfill the requirements established at the national and international markets for human consumption regarding size, form and weight.

Tubers were washed and in fresh form were ground in a mixed mill provided with blades and a 2.5 cm sieve for obtaining a uniform particle size.

For the formulation of the silages, raw matters were weighed in a CAMRY digital balance of 100 kg capacity.  They were deposited in four clean plastic tanks with a 450 kg capacity each.  Ingredients were added in the following order: silage 1) chopped tubers, natural yogurt and drinking water for human consumption (1_NY); 2) chopped tubers and whey (2_W); 3) chopped tubers, 5 % molasses B (83º Brix) and whey (3_WMB5) and 4) chopped tubers, 10 % molasses B (83º Brix) and whey (4_WMB10).

The ingredients were manually mixed homogenously with a wood spatula for 15 min at an environmental temperature of 24 ºC. Later they were introduced in the polyethylene microsilos with a capacity of 5 kg. The microsilos were closed according to the methodology of Ottati and Bello (1990). They were stored indoors protected from sunlight (Guevara et al. 1991). Samples for the analyses were taken according to the methodology of Tejada (1992).

The physicochemical indicators (temperature and pH) were assessed in 1152 microsilos at 0, 1, 2, 3, 4, 5, 10, 15, 30, 60, 90 and 180 d.  Twenty four microsilos were evaluated per treatment for totalizing 96 microsilos assessed each day of preservation.  Once realized the respective measurements the microsilos were thrown away.  Temperature of the microsilos was determined according the technique of Mier (2009) consisting of measuring the temperature at 20 cm depth.  After one resting hour for pH evaluation, watery extract was used made up of a fraction of 25 g of silage and 250 mL of distilled water (Cherney and Cherney 2003).

In the microorganism count the amount of fungi, yeasts and total coliform, Escherichia coli, Clostridium spp. and Salmonella spp. were determined at 0; 15; 30; 60; 90 and 180 d according with the procedures of Merck (2005).  A total of 192 samples of 200 g of the silage were collected in sterile transparent plastic containers with 250 g capacity.  Random samples were taken in 32 microsilos (eight per treatment) of the 96 evaluated on the physicochemical indicators at each preservation day. All determinations were made in triplicate.

The physicochemical and biological parameters were assessed through a simple completely randomized design.  The analysis of variance was made according to the recommendations of Steel et al. (1997). In the cases in which significant differences (P < 0.05) were found the means were compared by Duncan’s (1955) test.  Analyses were made through the application of the statistical program Infostat (Di Rienzo et al. 2012).

RESULTS AND DISCUSSION

At the opening time of the microsilos, no alcohol presence or decomposition symptom of the ensiled materials was observed. All microsilos had a sweet caramel coated smell.  Table 2 shows the temperature performance in silages of taro tubers.

There were no significant differences (P < 0.05) between treatments 2_W (22.65 ºC); 3_MB5 (22.64 ºC) and 4_MB10 (22.63 ºC) at the zero day of preservation.  These treatments surpassed the treatment with natural yogurt as inoculum source 1_NY (22.45 ºC).  However, at day one, treatments with natural yogurt 1_NY (22.53 ºC) and 5 % molasses B 3_MB5 (22.51 ºC) showed the highest temperature value (P < 0.05) differing from treatments 4_MB10 (22.24 ºC)  and 2_W (22.37 ºC) .  At days two and three there were no significant differences (P < 0.05) for the temperature of the treatments 1_NY (22.53-22.48 ºC)  and 2_W (2.53-22.49 ºC)  which was superior to 3_MB5 (22.23- 22.19 ºC)  and 4_MB10 (22.18-22.16 ºC), respectively.

Temperature from day four and until the 180 of evaluation was stable in all treatments.  The treatment in which molasses B at 10 % (4_MB10) attained the highest value (P < 0.05) of temperature (22.83– 22.54 ºC) and differed from 1_NY 22.38-22.46 ºC; 2_W 22.43-22.46 ºC)  and 3_MB5 (22.36-22.24).

In table 3 is shown the pH dynamics in silages of taro tubers.  The pH presented the highest values at the beginning of the fermentation process (day 0) in all treatments.  However, the (3_MB5) reached the highest value (P < 0.05) of this indicator (5.40).

From day one to four, pH decreased proportionally in all treatments (2_W) 0.71; (1_NY) 0.70; (4_MB10) 0.70 and (3_MB5) 0.69 units.  From day five to 180, pH stabilized with values between 3.95-3.88 (1_NY); 3.95-3.83 (4_MB10); 3.93-3.84 (2_W) and 3.93-3.83 (3_MB5).

The pH was maintained between the established ranges for producing silage of good biological quality.  The adequate pH indexes obtained in the four silage variants made possible that these latter were considered of optimum quality for its use in animal feeding. Well preserved silages presented values between 3.8 and 4.2.

The evaluation of the microorganisms is a premise, if the introduction of an animal feed is tried.  Thus, it is of vital importance knowing the sanitary stage of these microorganisms. Fungi, yeasts, total coliform and E. coli bacteria exhibited a concentration of (<10 CFU g^-1) at day zero of evaluation.  However, at 15; 30; 60: 90 and 180 d these microorganisms were absent in all treatments. Neither were there presence of Clostridium spp. or Salmonella spp. during the study.

In the variation of the temperature between treatments at the beginning of the fermentation process could have influenced the presence of the existing microflora in the yogurt, whey and molasses B of sugar cane (Caicedo et al. 2015).  These feeds have their own microorganisms that act with greater intensity producing heat.  Among the most important are the fungi, yeasts, bacteria and actinomycetes (Díaz et al. 2014).

In all silage variants of taro tubers, pH decreased until the fourth fermentation day and stabilized at the fifth.  Similar pH values reported Caicedo (2013) in silages of taro tubers until the 180 day of preservation (3.65).  In biological silages with the inclusion of variable levels of carbohydrate and protein sources, Maza et al. (2011) determined values between 3.63 and 3.75.  Morales (2012) obtained a value of 4.  Seemingly the great soluble carbohydrates availability of the taro tubers favored the rapid pH stabilization of the silages.

In silages with whey, ruminal contents or bovine feces, Díaz (2014) showed a pH decrease from the initial eight hours of the process with value of 5.77. This tendency was maintained until the final evaluation (96 h), with pH of 3.87 which influenced on other fermentation factors as the absence of coliform microorganisms.

pH is an indicator of great relevance in the fermentation processes. It is one of the most radical transformations occurring in the utilized material (Adedeji et al. 2011).  pH is closely related with the degradation processes taking place during preservation (Fagbenro and Jauncey 1998). When the silage has attained values between 3.8 and 4.2, it attains its stability (Lopes et al. 2013).  In this pH range, there is restriction of the development of proteolytic enzymes, enterobacteria and clostridiums (Tomich et al. 2004). The four variants of taro silage showed pH values which are between those recommended for this type of feed.

In the silages the concentration of < 10 CFU g^-1 of fungi, yeasts, total coliform and E. coli at day zero of assessment was determined. This can be associated with the external pollution of the tubers by the irrigation water systems, soil and organic fecal matter (poultry litter, swine litter) that can represent microbial pollution sources (Kozlowski 2007). However, in the continuous assessment until day 180 there was no presence of these microorganisms.

When the fermentation processes are adequate, sugars turn into organic acids, mainly in lactic acid and acetic acid, which are responsible for the fast pH fall that inhibits clostridium growth, responsible for great losses by the production of butyric acid in the silos (Posada et al. 2007 and Rendón et al. 2014).

In studies of Nikosi et al. (2009) with maize silage and in experiments of Nikosi et al. (2010) with potato an improvement in the aerobic stability of the silage with the inoculation of lactobacilli was observed. Nikosi and Meeske (2010) stated that the fermentation quality of the potato silage also improved with the addition of whey and molasses.

Possibly, results obtained in the inhibitory performance of Clostridium spp. and Salmonella spp. in the silages are directly related with the low pH of the silos under anaerobiosis conditions and before the presence of antimicrobial compounds produced by the lactic bacteria present in the fermentation processes (McDonald et al. 1991, Bello et al. 1993, Kozlowski 2007, Duniere et al. 2013 and Gismervika et al. 2015).

The lactic acid bacteria had positive effects on the silage characteristics among those cited are pH decrease, greater production of lactic acid, high DM digestibility, mainly on using homofermentative strains and greater aerobic stability on using heterofermentative (Filya 2003).

The biological competition among different types of bacteria responsible for generating different products and the lactic acid influence directly on the pH curve.  Elías et al. (1990) and García et al. (2005) found that lactic bacteria prevail due to the lactic acid production and of other short chain organic acids.

CONCLUSION

The four silage variants of taro tubers had a adequate performance of the physicochemical and microbiological indicators until day 180 being thus fit for animal feeding use.

ACKNOWLEDGEMENTS

Thanks are due to the National Secretariat of Higher Education for Science, Technology and Innovation (SENESCYT) of Ecuador for financing the development of this investigation.

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Received: March 23, 2015
Accepted: April 29, 2016

W. Caicedo, Universidad Estatal Amazónica, km 2 ½ vía a Napo, Pastaza, Ecuador. Email: orlando.caicedo@yahoo.es