Biological material
Ten bulk samples (1 kg each) of seeds were collected and transported to the DryLab-AORTech laboratories. Seeds were manually cleaned from foreign matter, eliminating broken or immature seeds, and the moisture was measured. The results ranged from 45.05 g/dm3 for control samples with 14.9% d.b. moisture and a mass of 100 seeds of 7.78 ± 0.13 g, to 36.43 g/dm3 for samples dehydrated for 1.5 h in DEM-LP, with a moisture content of 3.92 g/dm3 and 100-piece mass of 6.92 g4.
Dehydration methods
Thermo-solar system (TSD)
The internal conditions in the dehydration chamber were: the temperature oscillates between (44.1–66.4) °C and 1.00 ± 0.21 m/s air flux. After 45 min (0.75 h), the first sample was withdrawn to be analyzed, this had a moisture of 12.18% d.b. The second sample remained for 4 h having 2.30% moisture d.b. With this method, 2 h is required to reach the goal of 8% moisture (d.b.)4.
Dehydration by electromagnetic induction and low-pressures (DEMI-LP)
The heating chamber reaches 65 °C in 5 min, and the internal relative pressure can be reduced from the atmospheric pressure to approximately − 20 in Hg in 3 min, maintaining the chamber negative pressure concerning the atmosphere. The combination of low pressure and high temperature produces the evaporation of water, and in this process, the samples eliminate the moisture.
Samples of 1 kg at 14.95% 14.95% moisture (d.b.) of sunflower seeds, the first sample were dehydrated by 30 min (0.5 h) reducing to 10.43%, the second sample remained for 1 h, reaching 6.29% and the third sample was dehydrated by 1.5 h and the result was 3.92% moisture (d.b.), the necessary time to reach 8% of Moisture was 47 min4, then the all others chemical characterizations and few biological were carried out.
High-Resolution transmission electron microscope
Figure 1, shows the micrographs of the whole seeds, there can be seen how the hull fiber thickness was evaluated by a 200 μm microphotography analysis (500×), there had some changes in thickness, these detected changes explain why the volumetric expansion of whole seeds had increased by around 5%, as reported by Ortiz-Hernandez et al.4.
Transmission electron micrographs of sunflower seeds: (a) Control, (b) 4 h TSD, (c) 0.5, h and (d) 1 h DEMI-LP.
Viability of germination and growth
Table 1 shows the numerical results of the laboratory germination experiment, comparing the two selected drying methods and the different times, showing some interesting data, it can be seen the variation as the time of dehydration increases and moisture decreases, the germination variations are related to humidity and the relationship what time is just a consequence. This Table shows the loss of physiological quality of germination and grow viability, and also indicates that the loss of vigor occurs much faster when the germination decreases18.
The viability of seeds dehydrated for 0.5 h with the DEMI-LP method was the same as the control 66%, reducing to 40% after 1 h of dehydration. The lowest viability was obtained in seeds dehydrated for 4 h using the TSD method, just 24%.
Bromatological analysis
The percentual results obtained in the bromatological determination of the sunflower seeds are shown in Table 2. Even though the seeds were dehydrated, the humidity percentage was 10.4% in the sample 0.5 h DEMI-LP, 6.29% for 1 h DEMI-LP, and 2.31% in the sample 4 h TSD.
The percentage of ashes was higher in the sample 1 h DEMI-LP (4%), followed by 0.5 h in DEMI-LP (3.7%), and the lowest concentration was obtained in 4 h TSD (1.1%). This parameter indicates the amount of inorganic matter present in the samples14.
In Table 2 In accord with the results of nutrimental content in the sunflower seeds EE content was 35.7% in the control, decreasing in the dehydration treatments being the most notorious in the sample 0.5 h DEMI-LP with 31.7%.
The TOC content presented a maximum average value of 99.3% in 4 h by TSD and a minimum average of 97.7% in 1 h, in DEMI-LP. The importance of TOC derives from the decomposition of plants because it is used as a purity test on which bacterial growth and metabolic activities of living organisms or chemical compounds will depend as mentioned by Hendricks19, that is, the metabolic activity of the sunflower seed was not altered by the treatments used in dehydration.
Mineral analysis (macro and micro)
Table 3 presents the numerical results about minerals content, where the minerals concentrations in seeds are important for animal nutrition due to their vital function in the body. In the sunflower seed, the mineral contribution stands out due to its high content of P, K, Fe, and Zn.
Regardless of the dehydration method, Ca concentration in the control was 0.25% and increased as the dehydration time rose, on the other hand, the concentration of P decreased in the process of dehydration concerning the control (1.1%). This is probably due to the P volatility features. Phosphor in sunflower seeds is beneficial for the regulation of nerve impulses and intervenes in muscle activity, recommending its use to athletes or people who perform physical activities constantly20.
Iron is a mineral that occurs in high concentrations in dehydration treatments. In this analysis, the highest amount of Fe occurred in 4 h TSD (159.50 ppm). In comparison with Fe, the Zn concentration was lower after dehydration concerning the control (130.50 ppm). The nutritional requirement in ruminants can be covered through the consumption of sunflower seeds21,22.
Extraction and quantification of proteins.
The extraction of the polypeptide part of the proteins present in the hull and the kernel was determined; their concentrations are shown in Table 4.
In Table 4 the results of protein concentration are tabulated in function of type and time of dehydration, from this analysis where determined that the protein present in the hull is much lower and there is a loss drastically in both dehydration systems, 66.8% in 0.5 h and 23.7% in 1 h, boot in DEMI-LP and for TSD just keep 10.5% of the proteins in the hull. On the other hand, the concentration of proteins in the kernel control samples contain the highest concentration, with just 4 thousandths part (0.004) lower, in other words, keeps 99.1% of proteins with 0.5 h of DEMI-LP treatment while the samples with 1 h in keeps 98.4%, reduced the protein content 0.007 and for the sample with 4 h in TSD loss 0.022 µg for each microliter (μg/μg), compared with control data reaching 94.9% of the original protein content.
Protein electrophoresis of sunflower seeds tissues in polyacrylamide gels (PAGE-SDS)
The electrophoretic profiles are observed in Fig. 2.
(a) Protein gel of sunflower seeds, control, dehydrated (0.5 and 1 h) DEMI-LP and 4 h TSD. 1) Serine bovine albumin, 68 kDa molecular weight. 2) Hull Control, 3) Kernel control, 4) Hull 4 h TSD, 5) Kernel 4 h TS, 6) Hull DEMI-LP 0.5 h, 7) Kernel DEMI-LP 1.0 h, 8) Hull DEMI-LP 1.0 h, 9) Kernel DEMI-LP 0.5 h. (b) Graph illustrating the percentage and absolute value of each protein fraction, based on densitometric data from lane 2 of Fig. 2a.
Proteins densitometry
In lane 1 is the 68 kDa protein used as a reference. In lanes 4, and 8, there was no expression of protein bands indicating degradation by a dehydration protein weight between 32 and 68 kDa. The protein bands can be attributed to the α-β of 11S globulin (Helianthin) as mentioned by Molina23.
With the results of polyacrylamide gels in the sunflower hull it is noticed that lanes 2, 4, 6, and 8 have less intensity.
In Fig. 2, the percentage of equivalence of the bands after the analysis of densitometry expressed in protein at a concentration of 60 μg/μL of each sample, the values obtained from the densitometric analysis of the peel and almond bands of the sunflower seed are observed; the analysis of the data indicated a better comparison and a numerical appreciation of the bands. The total percentage of each lane in the bands is 100%. Observing from the almond sample in lane 3, the band of protein 4 has the highest percentage (24%) followed by bands 5 and 6 (20.7% and 16.1% respectively).
The protein densitometry numerical values are shown in Table 5.
During dehydration, proteins were under high temperatures and pressure being the probable cause of protein denaturation, where the data indicates that the amount of oxygen present in the process is very important.