ORIGINAL ARTICLE

Quality of Chopped and Ground Sweet Potato during the Production of Silage Feed for Pigs

Dr.C. Arelys Vázquez-Peña^I  , Dr.C. Antihus Hernández-Gómez^II  , Dr.C. Magalis Herrera-Villafranca^I  , Dr.C. Pedro Valdés-Hernández^II 

^IInstituto de Ciencia Animal, San José de las Lajas, Mayabeque, Cuba.

^IIUniversidad Agraria de la Habana, San José de las Lajas, Mayabeque, Cuba.

ABSTRACT

The size of the particles is one of the properties that have more influence in the quality of food for monogastric animals. The present work was carried out with the objective of evaluating the quality of the chopped and ground sweet potato during the production of silage feed for pigs in the plant “Héctor Molina", and to check if both characteristics fulfill the demands of the particle size recommended for this kind of food. To demonstrate if the particle size that is obtained coincides to that proposed for the chopping machine (40 ±7 mm)and for the hammer mill(4 ± 2 mm), the sweet potato is characterized physical and mechanically and two experiments are designed that use sweet potato samples of the same lot and in different schedules. The fractional sweet potato is measured with a vernier caliper and a sieve disperser-shaker is used for the finely milled one. A totally randomized design was utilized and Duncan Test for P <0,05 was applied in the necessary cases. For the analysis of the data, the statistical package Infostat version 2012 was used. It was determined that the sweet potato presents physical-mechanical characteristics in correspondence with the agroindustrial process and that the quality of the chopped and the ground sweet potato, respond to the proposed technology. It was also proved that the average value of the particle size was of 36,06 mm for the chopper apparatus and that 100% of the total mass of sweet potato fulfills the proposed particle size (4±2 mm).

Key words: Quality; Hammers Mill; Chopper Machine

INTRODUCTION

Feeding represents between 60 and 70% of the total cost of the porcine production systems, while the fattening (of 25 to 100 kg of weight live) consumes, approximately, 70% of the foods of the flock. Because of that, great importance is conceded to the rational and efficient use of the foods, since this aspect decides the general efficiency and the economy of these productive systems together with an appropriate flock management (^{Mederos et al., 2014}). Different types of nutrients compose the nutritious portions. They will be properly balanced to guarantee satisfactory growth, good reproductive yield, adequate immunologic condition and acceptable well-being. Energy sources represent the biggest proportion (60-80%) of the diet and they contribute the necessary energy to the animals. A great diversity of this type of foods exists. Sweet potato, cassava and banana are part of it.

Agroindustrial technologies developed in Cuba to transform raw material and to produce alternative foods for swine breeding are not based on soybean and corn. Industrial Saccharine, finished liquid fodder (PLT), protein honey, silage of fish, silage of vegetables and the creole fodder are diverse. The agroindustry to produce Cuban Silage Food (CSF), starting from the mixture of thermalized Saccharomyces cerevisiae yeast cream, honey B of the sugarcane, concentrated vinasse and sweet potato (Ipomoea batata (L. )Lam.), it is composed by the areas of weighting, reception and storage of raw materials, transportation and milling, mixing, silage and dispatch (^{Vázquez, 2019}). Among the main approaches that intervene in the selection of the equipment that compose each of them are the characteristics of the technological process, the activities carried out, the production capacity, the work conditions, the levels of noise and allowed vibration and the energy consumption (^{Sablikov, 1978}; ^{González, 1993}; ^{Sotto, 2000}; ^{Polanco, 2007}; ^{Ortiz et al., 2011}; ^{Olivet et al., 2012}; ^{Stout, 2012}; ^{Paneque et al., 2018}). All these approaches to obtain maximum security, technical-economic efficiency, warranty of the work for the environmental conditions of the place and the mechanization of the process (^{Paneque, 1988}; ^{Pahl et al., 2005}).

For the selection of the equipment that participate in the milling process, the aspects before mentioned are taken into account, as well as the productivity of the machines, the dosage form, the chemical and physical-mechanical characteristics of the sweet potato, the particle size to obtain, milling type (humid or dry) and the dimensions and cleaning of the proposals (^{Iglesias and Soto, 1987}; ^{Pahl et al., 2005}; ^{Paneque et al., 2018}).

The size of the particle is an important factor in the quality of the finished product, the fabricators of foods for animal consumption should consider the relationship between it and the form of the food. The chopper machines are very useful, when the raw materials to process are heterogeneous and its appropriate selection is important to assure the wanted size (^{Valdés, 2008}; ^{Valdés et al., 2010}, ²⁰¹²). The mills are used to mill vegetable mass and agricultural products and they are considered one of the most important equipment in the agroindustrial processes for the elaboration of foods balanced for the animal production, (^{Iglesias and Soto, 1987b}; ^{Valdés, 2008}; ^{Paneque et al., 2018}).

The present work was carried out with the objective of evaluating the quality of the chopped and ground sweet potato during the production of silage feed for pigs in the plant “ Héctor Molina", and to check if both fulfill the demands of the particle size recommended for this food type.

METHODS

Determination of the Main Physical-Mechanical Properties of the Sweet Potato

To determine the physical-mechanical properties of the sweet potato (size measuring: length and perimeter, mass, resistance to the penetration and rolling angle) and for visual exam, 30 samples taken at random from 5 different lots were used. The measurements were carried out in the area of Engineering in the Institute of Animal Science (ICA), to an average temperature of 23, 9^oC, atmospheric pressure of 100,72 kPa, relative humidity of 73,8% and a MS of 27% in the different sweet potato lots.

The size was determined by means of the methodology described by ^{García & Pacheco (2008)} and ^{Palomino et al. (2010)} and for this a measuring-tape of glass fiber, Stanley type of 3 m long, with 0,1 mm of precision and vernier caliper (range 0-350 mm) with 0,05 mm of precision were used.

The resistance to the penetration was determined by means of the methodology described by ^{García & Pacheco (2008)} and a Penetrometer Wagner Instruments, model FT-40, with ±1 of precision was used with a stainless steel beveled cutting needle resistant to the corrosion, and a 6 mm tip. The measurements were made in three points of the lateral face, as close to the equatorial area as possible and 120° distant one from another, with presence of the periderm (^{Castro et al., 2007}), for a total of 90 measurements. The resistance to the penetration was determined (N/mm²), according to methodology used by ^{García & Pacheco (2008)}.

The rolling angle was determined with an inclined plane, Scala brand and 0,05º of precision that allowed with a graduate scale from 0 to 90º, carrying out the reading of the inclination angle of the surface when the sweet potato begins to rotate.

Under the conditions before described, the volumetric mass (t/m3), the density of the material (g/cm3) and the efficiency of the filling were determined. For that, sweet potatoes of the studied variety (INIVIT B-98-3), of three different lots were used and three repetitions were made for each of the determinations.

To determine the volumetric mass of the sweet potato, the methodology used by ^{Valdés (2003)} was followed and for that 500 kg of sweet potato were selected. A digital scale of platform (GADGETS) with maximum capacity of 500 kg, 100 g of precision and a cylindrical recipient of galvanized sheet N° 14 of 0,5 m³ was used. The sweet potatoes that fitted in the recipient were weighted with the scale and to the results of the experiment the volumetric mass of the sweet potato was determined by the following expression:

$\gamma =\frac{Q}{V}$

where:

γ -	Volumetric mass , t/m^3;
Q -	mass of the sample, t;
V -	volume occupied by the sweet potato in the recipient, (0,5 m3).

The density of the sweet potatoes was determined according to the methodology described by ^{Iglesias and Soto (1987)}, to do that, 1 kg of sweet potato was selected, determining its mass with a technical scale Scout Pro of accuracy 0,01 g. The sweet potatoes were cut in segments, which were submerged in a graduate test tube of 1 L, with 1 cm³ of accuracy.

With the difference of the volume of water (∆Vb) displaced by each sweet potato segment it was determined for each test the density by means of the expression:

${\rho }_b{}_{}=\frac{m_{sb}{}_{}}{\Delta V_b}$

where:

ρb -	density of the sweet potato segment, g/cm3;
msb -	mass of the sweet potato segment, g;
ΔVb -	volume of the sweet potato segment, cm3

The efficiency of filling (β) is determined according to the methodology described by ^{Paneque (1988)}, using the following equation:

$\beta =\frac{h_2}{h}$

It started from knowing the dimensions of the receiving hopper of sweet potato (Figure 1), the distribution of the sweet potatoes in it, the angle of inclination of the transporter mat of splints with lateral borders (20°) and the correction factor (C1 = 0,95).

FIGURE 1 Simplified representation of transporter of splints with lateral borders. 

To determine the bank angle (φ) an experiment with the conditions described before was carried out, according to the methodology described by ^{Paneque (1988)}. Six samples of sweet potato (INIVIT B-98-3) of 15 kg each from two different lots were taken. They were let fall freely on a horizontal plane, the space was defined to a width (b = 0,56 m) that was 0,8 times the width of the rubber band (Bp). The area was simulated the most real possible because the rubber band goes on plane rollers. The height was measured with a millimeter rule and the information (H) was picked up in chart. The dispersion and position statistics were determined to data with the statistical package Infostat version 2012 (^{Di Rienzo et al., 2012}).

Determination of Quality of Chopping and Grinding Processes

The chopper machine proposed to achieve the chopped sweet potato (40 ±7 mm) has two organs of work, type drum that move to an angular speed of 36,6 rad s^-1, each one with two sets of interchangeable blades (650 mm long and 100 mm of diameter) and screwed at 90° (Figure 2). It presents a productivity of 10t/h, with electric motor of 22 kW and a rotation frequency of 900 rpm.

FIGURE 2 Simplified diagram of chopper machine fed from transporter of rubber band. 

The mill of hammers recommended to achieve the particle size (4±2mm) and to guarantee the established production levels, works to an angular speed of 182,8 rad s-1, it presents hammers with edges in the ends and in both faces, with possibility of inverting and changing them, what allows milling sticky material (^{Paneque et al., 2018}). This mill (Figure 3) with supports and interchangeable sieve is of easy cleaning. It works with an electric motor with a power of 45 kW, frequency of rotation of 1 800 rpm and it is fed by free fall from the chopper machine.

FIGURE 3 Simplified diagram of mill of hammers. 

To check if the particle size that is obtained in the agroindustry corresponds to that proposed for the chopper machine and the hammer mill, two experiments were designed that were developed in the laboratory of the production plant of SF of Héctor Molina Riaño in Mayabeque, where the conditions and necessary means for this end were created. They were: an average atmospheric temperature of 23,9^oC, an atmospheric pressure of 100, 72 kPa, relative humidity of 73, 8% and a percentage of MS in the samples of 27%.

To analyze the particle size, a study was carried out with the following characteristics: Sweet potato of the variety INIVIT B-98-3, of a same lot was used and samples were taken at different times (8:00, 11:00, 13:00, 15:00 and 17:00), to check if there were variations on the chopped particles’ size according to the time.

The mass of the samples (2,2 kg) was determined because the sweet potato is 40% of the composition of the SF and the pig consumes an average of 5,5 kg of it. The sample to process, to be representative, has to be equivalent to the sweet potato that is inside the SF and that should be consumed by the pig in one day. The mass of the samples was obtained with a technical scale Scout Pro, with ±0,1 g of precision and range up to 5 000 g.

To check if there were significant differences in the sizes of particles in the schedules, a totally randomized design was used and a Duncan Test was applied for P <0,05 in the necessary cases. For the analysis of the data, the statistical package Infostat version 2012 was used (^{Di Rienzo et al., 2012}).

Experiment N°. 1. Determination of the size of the fractional sweet potato that was obtained with the chopper machine with organ of work type drum and blades

The determination consisted on measuring with vernier caliper of range 0-250 mm and accuracy 0,05 mm, all the fractions of sweet potato of five samples (of 2,2 kg each one) from the same lot, in the previously established schedules. The sweet potato fractioned by the chopper of blades was always measured by the biggest of its sides.

Experiment N°. 2. Determination of the particle size that was obtained with the hammer mill

The content of humidity in dry base before the sieving was determined by the expression that appears next. For that, the samples obtained in the laboratory of the agroindustry were dried at 60ºC for 24 hours, by using a thermostatic stove Boxun: RT: 250 ± 5ºC, accuracy of 0,1ºC.

$CH=\left(\frac{H_i-H_f}{H_f}\right).100$

where:

CH -	content of humidity in dry base, %;
Hi -	humid initial mass, kg;
Hf -	final dry mass, kg.

For this experiment a sieve disperser -shaker of interchangeable mesh, Clarke brand was used. Five samples of 2,2 kg were selected (to be the sweet potato 40% of the portion of the SCF that consumes a pig in the day) each one from the same sweet potato lot and in the schedules proposed to guarantee similar conditions of humidity, the samples were weighed in a technical scale Scout Pro accurately of ±0,1 g and range up to 5 000 g. The methodology described by ^{Valdés (2008)} was used. That consists in removing the sweet potato milled in a sieve of caliber 7 mm during 1 min, which allows that particles with average dimensions of 6 mm pass through it, with the objective of estimating the means of the mass (kg) of sweet potato milled by the hammer mill in the established schedules. A time of useful work of 12 min was used in every schedule.

Later, the bottom was changed for a mesh of caliber 5 mm (particles with average dimensions of 4 mm) and the mass of milled sweet potato that was in the sieve in the different schedules was quantified (kg), with the objective of estimating its mean.

RESULT AND DISCUSSION

Main Physical-Mechanical Characteristics of Sweet Potato

The physical-mechanical characteristics (Table 1) showed a size of big proportions and irregular form, being feasible for their agroindustrial processing. The consumers look for roots of medium sizes with not very irregular forms (^{García et al., 2016}). The resistance to the penetration was comparable with that of other roots and tubers, being a root of hard bark, similar to cassava bark (^{Rodríguez, 2008}). The rolling angle was low, given that the unequal rounded form facilitated that it rotated to few degrees of inclination.

TABLE 1 Main physical-mechanical characteristics of sweet potato 

Indicators		Means	DE	CV, %
Size	long (mm)	147,35	34,21	23,21
	Perimeter (mm)	286,07	85,61	29,92
Mass (kg)		0,607	0,219	36,07
Resistance to penetration (N/mm^2)		6,61	0,11	1,66
Rolling angle (º)		21,6	0,69	3,19
Volumetric mass (t/m^3)		0,750	0,01	1,33
Density (g/cm³)		0,7508	0,011	1,46

DE: Standard deviation. CV: Variation coefficient.

The efficiency of filling (β) was of 0, 8, similar for the three repetitions. A triangle similar to that of the Figure 1was formed. The bulk load was deposited in a transporter of splints with lateral borders.

From the experimental results, it was obtained that the slope angle was of 47,08°. The confidence interval was calculated and it was observed that for an estimate of the height (H), the mean obtained was of 0,1908 m. That evidenced that with a confidence of 95%, that value was in the interval of 0,18 and 0,20 m (Table 2).

TABLE 2 Sweet potato height for each sample from both lots 

Variable	Lot 1			Lot 2			EE(±) Signif.
	1	2	3	1	2	3
Height H (m)	0.19	0,20	0,185	0,18	0,193	0,197	0,03 P=0,7132

Determination of the Quality of the Chopping and Grinding Processes

The results of the variance analysis for the particle size obtained with the chopper machine are shown in Table 3. From this study it is possible to affirm that the factor schedule of sampling did not have a significant influence on the size of the particles obtained in the chopping process. Other factors like variety, product humidity, hardness and resistance to the cut and the technological parameters as the power and speed of the work organs, influence directly on the parameter of quality in study ( ^{Paneque et al., 2018}). It evidenced that the schedule did not influence in the particle size that was of 40±7 mm.

TABLE 3 Size of particles obtained by the chopper machine 

Hour / Variable	8:00	11:00	13:00	15:00	17:00	EE(±) Signif.
Mean value of the particles (mm)	39,20	34,20	38,60	34,40	33,80	4,01 P=0,7857

When calculating the interval of confidence of the particle size for this experiment, it was observed that the mean value was of 36,06 mm, which was in the interval of 32,52 and 39,56 mm with a level of confidence of 95%, (Table 4). That means that it was in the range (40±7 mm).

TABLE 4 Interval of confidence of the particles size in mm 

Particle size	EE(±)	LI (95%)	LS (95%)
36,06	1,71	32,52	39,56

When analyzing the quality of the sweet potato milled starting from the size of particles obtained by means of the sieving, it was observed that the percentage of mass retained in the sieve caliber 7 mm was similar to zero. However, when carrying out the test in the sieve of caliber 5 mm, it was observed that there were not significant differences among the schedules of samplings (P=0,7059), (Table 5).

TABLE 5 Percentage of milled sweet potato retained in the sieves of calibers 7 and 5 mm 

Schedule	8:00	11:00	13:00	15:00	17:00	EE (±) Signif.
Milled sweet potato retained (%), in sieve of caliber 7 mm	0	0	0	0	0	0
Milled sweet potato retained (%) ,in sieve of caliber 5 mm	10,45	10,45	12,27	10,90	9,54	0,03 P=0,7059

The same as in the previous experiment, the interval of confidence was calculated and it was observed that for an estimate of the sweet potato mass the average that stayed in the sieve of caliber 5 mm was of 0,24 kg, what evidences that, with a confidence of 95%, that value is respectively in the interval of 0,21 and 0,26 kg, which represents 10,9% of the total mass (Table 6).

TABLE 6 Calculation of the interval of confidence for the mass of sweet potato in kg 

Sweet potato mass	EE(±)	LI (95%)	LS (95%)
0,24	0,01	0,21	0,26

As a result it was obtained that under the studied conditions, in all the samples of the five schedules, 100% of the particles passed through the sieve of caliber 7 mm (none possesses superior value to 7 mm) and only 10,9% of these was retained in the sieve of caliber 5 mm. That demonstrated that the selected equipment (chopper machine and mill of hammers) in the technological proposal, under the studied conditions, are able to produce the particle size recommended for the feeding of pigs, according to their management requirements. It was proved that the particle size obtained by the chopper machine and the mill of hammers corresponds to the proposed technology. The results obtained evidenced that.

CONCLUSIONS

• It was proved that sweet potato presents physical-mechanical characteristics in correspondence with the established parameters for its agroindustrial processing, as it presents a size of big proportions, with resistance to the penetration of 6,61 N/mm² and angle of rolling of 21,6º.

• The quality of the chopped sweet potato during the production of silage feed for pigs in the plant “Héctor Molina” under the studied conditions, responds to the proposed technology, being proven that the average value of the particle size was of 36,06 mm.

• It was obtained that the quality of the milling responds to the demands of the technology, demonstrating that 100% of the total mass of sweet potato fulfills the recommended particle size (4±2 mm) and that only 10,9% of the particles has a value between 4 and 6 mm.

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6The mention of commercial marks of teams, instruments or specific materials obey identification purposes, not existing any promotional commitment with relationship to the same ones, neither for the authors neither for the editor.

Received: December 12, 2019; Accepted: September 25, 2020

^*Author for correspondence: Arelys Vázquez-Peña, e-mail: [e-mail]

Arelys Vázquez-Peña, Investigadora, Instituto de Ciencia Animal, San José de las Lajas, Mayabeque, Cuba, e-mail: [e-mail]

Antihus Hernández-Gómez, Profesor Titular, Universidad Agraria de La Habana, San José de las Lajas, Mayabeque, Cuba, e-mail: [e-mail]

Magalis Herrera-Villafranca, Investigadora, Instituto de Ciencia Animal, San José de las Lajas, Mayabeque, Cuba, e-mail: [e-mail]

Pedro Valdés-Hernández, Profesor Titular, Universidad Agraria de La Habana, San José de las Lajas, Mayabeque, Cuba, email:[e-mail]

The authors of this work declare not to present conflict of interests.