Received: July 13, 2022
Accepted: December 12, 2022
Available: December 22, 2022
Due to the high genetic variability of the potato, the starch can exhibit different properties of interest to the industry. With the present investigation, it is intended to know these differentiating characteristics in comparison with commercial sources that can be useful in different sectors. Therefore, the objective of this research was to establish a comparison between potato starches extracted from native varieties (Solanum phureja) with commercial potato and corn starches. A physicochemical analysis was carried out, for which characteristics such as amylose content, phosphorus, resistant starch (RS), slow digestibility starch (SDS), rapid digestibility starch (RDS), granule shape, granule size and crystallinity were evaluated. The technofunctional analysis included variables such as amylographic, thermogravimetric and differential scanning calorimetry analysis. The starches of the native varieties exhibited differential characteristics with respect to the commercial starches. Andina variety obtained the highest peak viscosity (8714 cP), followed by Ratona Blanca starch (6148 cP). In addition, these two varieties had the highest content of resistant starch (33.14±0.8) % and (28.9±0.7) % respectively), higher content of amylose (33.9 % and 35.5 % respectively), phosphorus (>0,08 % for both varieties), high crystallinity and higher enthalpy values (> 19 J/g for both varieties), which make them materials of potential use in different industries. The correlations presented between variables such as resistant starch (RS), enthalpy and crystallinity, showed possible differences at the structural level, which highlighted the differential characteristics of each starch.
Keywords: Amylose, amylographs, X-ray diffraction, digestibility, thermal properties.
Debido a la alta variabilidad genética de la papa, el almidón puede exhibir diferentes propiedades de interés para la industria. Con la presente investigación se pretende conocer esas características diferenciadoras en comparación con fuentes comerciales que pueden ser de utilidad en distintos sectores. Por eso, el objetivo de este estudio fue establecer una comparación entre los almidones de papa extraídos de variedades nativas (Solanum phureja) con los almidones comerciales de papa y maíz. Se realizó un análisis fisicoquímico, para lo cual se evaluaron características como contenido de amilosa, fósforo, almidón resistente (RS), almidón de digestibilidad lenta (SDS), almidón de digestibilidad rápida (RDS), forma de gránulo, tamaño de gránulo y cristalinidad. El análisis tecnofuncional incluyó variables como análisis amilográfico, termogravimétrico y calorimétrico diferencial de barrido. Se halló que los almidones de las variedades nativas exhibieron características diferenciales con respecto a los almidones comerciales. La variedad Andina obtuvo el pico de viscosidad más alto (8714 cP), seguido del almidón Ratona Blanca (6148 cP). Además, estas dos variedades presentaron el mayor contenido de almidón resistente (33,14±0,8) % y (28,9±0,7) %, respectivamente), mayor contenido de amilosa (33,9 % y 35,5 %, respectivamente), fósforo (>0,08 % para las dos variedades), alta cristalinidad y mayores valores de entalpía (> 19 J/g para las dos variedades), lo que los convierte en materiales de potencial uso en diferentes industrias. Las correlaciones presentadas entre variables como almidón resistente (RS), entalpía y cristalinidad, evidencian posibles diferencias en lo estructural, lo que exaltó las características diferenciales de cada almidón.
Palabras clave: Amilosa, amilógrafos, difracción de rayos X, digestibilidad, propiedades térmicas.
Starch is one of the most abundant polysaccharides in nature. It is composed mainly of two glucose polymers: amylose and amylopectin [
The physicochemical, functional and digestibility properties of native starches will be influenced, among many reasons, by their granular structure, their composition, their botanical source and the extraction method used [
Other sources of starch are tubers and roots such as potatoes and cassava [
For the year 2020, Colombia produced about 2.6 million tons of potatoes [
Starches from unconventional botanical sources such as native potato may exhibit desirable properties of importance [
The comparison of starch from native potato varieties with commercial materials is relevant to establish differences and similarities that may be useful at an industrial level. The research of [
So far, there are no reports comparing starches from native potato varieties of Nariño with existing starches on the market. Hence, the objective of this research was to evaluate some physicochemical and technofunctional properties of starch from two native potato varieties: Ratona Blanca and Andina, with commercial potato and corn starches. Therefore, it seeks to determine the potential of these processes as a processing alternative. And thus, the planting of native potato varieties could be stimulated again and prevent their genetic loss.
2.1 Raw Material
Two varieties of native potato (Solanum phureja) grown in the municipality of Gualmatan in the department of Nariño were used. The samples of the Ratona Blanca and Andina varieties were selected, classified, and cleaned for further processing.
2.2 Potato Starch Extraction and Commercial Starches
Starch from native variety potatoes was extracted according to the methodology described by [
2.3 Physicochemical Properties
Starch was analyzed to determine amylose and phosphorus content with the techniques reported by [
2.4 Pasting Properties
Pasting properties of starch were carried with a TA Instruments AR1500 rotational rheometer, following the methodology reported by [
2.5 Thermal Properties
Thermal properties were analyzed using a TA Instruments DSC Q20 differential scanning calorimeter, 2 mg of starch was weighed into an aluminum pan and water (1:3 w/w ratio, dry basis) was added. The containers were hermetically sealed. A period of thermal equilibrium was continued for 2 hours before analysis. The samples were gradually heated at 10 °C/min following a temperature ramp from 20 °C to 200 °C. Through the thermograms (DSC) obtained, the initial or start gelatinization temperature (To), peak gelatinization temperature (Tp), final gelatinization or melting temperature (Tc) and the enthalpy of gelatinization (ΔH) were determined.
The TGA analysis was carried out in the Q50 thermogravimetric equipment brand TA Instruments. The starting temperature of starch thermodegradation was obtained with samples of (6 ± 0.50) mg in the presence of a nitrogen atmosphere. A heating of 5 °C/min was carried out, until reaching 600 °C.
2.6 In-vitro Digestibility
The digestible and resistant fractions of starch were quantified with the enzyme kit from Megazyme (Megazyme International Ireland Ltd. Co. Wicklow, Ireland) K-DSTRS 11/19. Rapidly digestible starch (RDS) and slowly digestible starch (SDS) were calculated with (1). Resistant starch (RS) was calculated with (2).
Where:
DA = absorbance read after 20 minutes (RDS), after 120 minutes (SDS).
F = absorbance conversion to mg.
EV = extraction volume (mL).
W = Weight of the analyzed sample.
Where:
DA = absorbance read against the reagent blank.
F = absorbance conversion to mg
EV = extraction volume. (mL)
FV = aliquots taken from the final volume
W = weight of the analyzed sample in g
2.7 Statistical Analysis
In the experimentation, a totally random experimental design was used. Statistical analysis was carried out using an analysis of variance (ANOVA). For this, a Tukey test at 95 % confidence was used to determine if there were differences between the properties of the studied starches (Andina, Ratona Blanca, commercial potato and corn). Data are reported as the mean of four replicates ± the standard deviation.
Additionally, a Pearson correlation analysis was performed on some of the variables studied to determine the statistical relationship between them. All analyzes performed were run using RStudio software.
The results of the physicochemical parameters evaluated for potato starch varieties Ratona Blanca and Andina in comparison to commercial potato and corn starch are shown in Table 1.
Parameter | Native potato starch | Commercial potato starch | Commercial corn starch | ||
Ratona Blanca | Andina | ||||
Phosphorus (%) | 0.08 ± 0.00c | 0.09 ± 0.00d | 0.06 ± 0.00b | 0.02 ± 0.00a | |
Amylose (%) | 35.50 ± 2.80c | 33.90 ± 3.30c | 24.20 ± 2.10b | 21.50 ± 2.50a | |
Size | Major axis (µm) | 16 - 84c | 27 - 66d | 4.6 - 53b | 10 - 20a |
Minor axis(µm) | 1 - 82d | 1 - 66c | 2 - 39b | 2 - 20a | |
Crystallinity (%) | 23.99 ± 0.60b | 22.94 ± 0.20b | 24.76 ± 0.20c | 17.45 ± 0.40a |
3.1 Phosphorus and Amylose Content
The phosphorus content is higher in the starch of the two potato varieties compared to commercial potato and corn starch. There were statistically significant differences between the sources evaluated (P<0.05). The potato starch variety Ratona Blanca presented higher values of phosphorus (0.08 %), only slightly surpassed by Andina (0.09 %). Several authors have reported a phosphorus content in potato starch of up to 0.06 % and a maximum content in corn starch of 0.03 % [
Amylose content in the two potato varieties was higher than that found for commercial potato and corn starch, with significant differences between these two botanical sources (P<0.05). Starch from the Ratona Blanca variety had a higher amylose content, while corn starch had the lowest content among all the starches studied. The values found are close to the normal content of amylose in starch of different potato cultivars (20 % to 35 %) reported by [
The results found in the present investigation are greater than those reported by [
3.2 Scanning Electron Microscopy (SEM)
Figure 1 shows the micrographs of the starch granules evaluated. It was observed that the size and shape distribution of the potato starch granule is not uniform. The varieties studied exhibit large and oval granules and smaller spherical granules (Figure 1(a), 1(b)). What was found coincides with [
As seen in Table 1, the Ratona Blanca variety presented a larger size compared to the Andina variety and to commercial potato and corn starches. The diameters obtained for the two native potato varieties were higher than those reported by [
The variation in size and shape of the starch granules are attributed, among other reasons, to the botanical source [
3.3 X-ray diffraction
Figure 2 shows the X-ray diffraction patterns of potato and corn starches. The starch of the two potato varieties and the commercial potato starch presented a B-type crystalline structure. Corn starch presented a type A diffraction pattern with a doublet around 17.15° and 18.06° of 2θ. It also exhibited strong diffraction peaks around 15.11° and 23.03° of 2θ.
Potato starch from native varieties showed higher intensity peaks at 17° of 2θ (Figure 2). Likewise, they presented a peak at 5° of 2θ which has been reported as characteristic of starches with type B crystallinity [
The analyzed starches presented differences between the potato varieties with the commercial starches (P<0.05). Commercial potato starch presented the highest crystallinity with approximately 25 % (Table 1). While corn starch presented the lowest crystallinity with an approximate value of 17 %. These results are in agreement with [
Type B crystallinity starch are longer and are grouped in a hexagonal cell [
3.4 Pasting Properties
The pasting parameters were different among all the starches evaluated (P<0.05). As shown in Figure 3, the Andina variety exhibited the highest peak viscosity (PV), with (8714 ± 166) cP. While corn starch exhibited the lowest result (1241 ± 79) cP. For its part, potato starch variety Ratona Blanca presented a higher PV (6148 ± 153) cP than corn starch and commercial potato starch (5346 ± 129) cP.
Pasting temperature (PT) was higher for corn starch, followed by Ratona Blanca, with values close to 75 °C and 64 °C, respectively. While the commercial potato starch and the Andina variety presented PT of 63 °C and 62.2 °C, respectively. A higher PT refers to a higher internal organization of the starch granule [
The lowest values of setback viscosity (SV) were again for corn starch and potato variety Ratona Blanca with 104 cP and 310 cP respectively. On the other hand, the highest final viscosity (FV) was exhibited by Ratona Blanca starch (5838 cP), while the lowest value was for corn starch (1137 cP). The setback viscosity (SV) is related to the ability of starch to retrograde (syneresis) and the final viscosity (FV) refers to the ability of starch to form viscous pastes [
On the other hand, authors of [
3.5 Thermal Properties
The gelatinization parameters of the starches analyzed by DSC are shown in Table 2. The initial temperature (To) of potato starches was lower compared to corn starch, indicating that more energy is required to initiate gelatinization [
Starch | To (°C) | Tp (°C) | Tc (°C) | ΔH (J/g) | Tc-To (°C) | Max deg T° (ºC) | Residual mass (%) |
Ratona Blanca | 57.4±0.5b | 63.4±0.2c | 71.2±0.5c | 21.3±0.2c | 13.8±0.5d | 317.2±0.5a | 8.1±0.2b |
Andina | 56.3±0.4a | 60.5±0.3a | 68.9±0.3a | 19.7±0.2b | 12.6±0.1c | 320.7±0.6b | 12.25±0.4c |
Commercial potato | 58.3±0.5c | 62.1±0.5b | 64.1±0.4b | 19.4±0.5b | 7.6±0.5b | 320±0.9b | 6±0.1a |
Corn | 70.5±0.2d | 74.6±0.4d | 79.1±0.4d | 10.1±0.5a | 6.6±0.5a | 327.7±0.8c | 6.4±9.2a |
Comparatively, potato starch needs the most energy to alter the semi-crystalline structure of the granules. This agrees with the crystallinity exhibited by potato starches compared to corn starch. Especially Ratona Blanca potato starch exhibits higher ΔH, possibly due to its crystallinity and internal structure. The gelatinization range (Tc - To) was narrower for corn starch, while it was wider for the Ratona Blanca variety. The small range of gelatinization may be due to the presence of less thermally stable crystallites within the starch granules [
The TGA results of the potato and corn starches are presented in Table 2. The weight loss was generated in two stages, the first one occurred around 100 °C and corresponds to the elimination of water in the sample. The second stage occurred between 250 °C - 370 °C, which was attributed to starch decomposition. The degradation start temperatures were close among all the starches evaluated. Ratona Blanca variety presented a maximum degradation temperature lower than the other starches. This means that the variety mentioned is thermally stable at temperatures below 317 ºC where the process of thermal degradation begins. Regarding the residues, after the thermal process, the starch of the Andina variety was the one with the highest residual percentage.
The residue corresponds to the inorganic components of starch [
Different authors such as [
The thermal degradation of starch is a relevant aspect when processing foods and starch-based materials, especially in processes associated with high temperatures [
3.6 In-vitro Digestibility
Figure 4 shows the results for the digestibility parameters evaluated: Rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). Highly significant differences (P<0.001) were found between the starches studied, in all digestibility fractions analyzed, except for slowly digestible starch (SDS). The RDS was significantly lower in potato starch from native varieties compared to commercial starches. With values of (71.47±0.76) % and (67.8±0.8) % for commercial corn and potato starches, respectively. On the other hand, potato starch varieties Andina and Ratona Blanca presented contents of (57.7±0.2) % and (52.6±1) %, respectively.
Potato starches presented SDS values close to 12 % for all starches with the exception of corn starch, which presented values close to (7.5±0.3) %. The content of resistant starch (RS) was higher in starches from the Ratona Blanca and Andina varieties, with (33.14±0.8) % and (28.9±0.7) %, respectively.
While commercial potato starch only obtained a content of (22.5±0.7) % and (11.8±0.5) % for corn. The results found were similar to the RS values reported by [
3.7 Correlation and Comparison Between Physicochemical and Functional Properties of Potato and Corn Starches
Table 3 shows the correlation coefficients. Variables that did not show correlation or that were represented by other variables such as TGA parameters and granule size were excluded.
Amy | RS | Cryst | Tc | Tp | To | ΔH | PT | PV | FV | BV | SV | P | |
Amy | 1.00 | *** | * | - | * | ** | ** | - | ** | ** | - | - | *** |
RS | 0.89 | 1.00 | ** | - | *** | *** | *** | *** | *** | ** | - | - | *** |
Cryst | 0.52 | 0.79 | 1.00 | *** | *** | *** | *** | *** | ** | - | - | - | ** |
Tc | -0.27 | 0.55 | 0.92 | 1.00 | *** | *** | *** | ** | - | - | ** | * | ** |
Tp | -0.63 | 0.83 | 0.93 | 0.89 | 1.00 | *** | *** | *** | *** | - | *** | ** | *** |
To | -0.71 | 0.90 | 0.93 | 0.84 | 0.99 | 1.00 | *** | *** | *** | - | ** | * | *** |
ΔH | 0.71 | 0.93 | 0.95 | -0.80 | -0.94 | -0.98 | 1.00 | *** | *** | * | * | - | *** |
PT | -0.64 | -0.85 | -0.94 | 0.89 | 0.99 | 0.99 | -0.96 | 1.00 | *** | - | *** | ** | *** |
PV | -0.75 | 0.85 | 0.76 | -0.69 | -0.93 | -0.93 | 0.86 | -0.92 | 1.00 | - | *** | *** | *** |
FV | 0.78 | 0.79 | 0.36 | 0.01 | -0.32 | -0.46 | 0.57 | -0.36 | 0.40 | 1.00 | - | * | |
BV | 0.44 | 0.50 | 0.55 | -0.66 | -0.80 | -0.73 | 0.58 | -0.76 | 0.87 | -0.08 | 1.00 | *** | ** |
SV | 0.31 | 0.34 | 0.43 | -0.58 | -0.69 | -0.60 | 0.43 | -0.64 | 0.78 | -0.23 | 0.98 | 1.00 | * |
P | 0.83 | 0.95 | 0.79 | -0.64 | -0.92 | -0.95 | 0.92 | -0.91 | 0.97 | 0.60 | 0.73 | 0.61 | 1 |
Amylose content had a positive correlation with resistant starch, crystallinity, phosphorus, ΔH and FV. While it also presented negative correlations with variables such as Tp, To and PV. Starch resistance has often been associated with amylose content. The denser structure of amylose in relation to amylopectin makes it less susceptible to enzymatic attacks [
Similarly, the crystallinity that in most cases is negatively affected by amylose; in the present investigation it exhibits a positive relationship, possibly due to its length and disposition. In general, starches with higher crystallinity can become more resistant. In this study, there was a positive correlation between these two variables (r: 0.79; P<0.01).
This is evidenced by the higher RS content of potato starches, which in turn presented higher crystallinity. However, it has been determined that the starch resistance does not always depend on the degree of crystallinity [
The inverse correlation presented between amylose and PT was also reported by [
The higher viscosity of the Andina variety starch can be attributed to factors such as its higher content of amylopectin and phosphorus, or a possible higher proportion of larger granules [
Studies reported by [
Enthalpy (ΔH) was positively correlated with amylose content, RS, and crystallinity. Authors such as [
The variation of the composition and conformation at the molecular level has a significant impact on the functionality of the starch. These are given among other reasons at the botanical source of origin. According to [
The Ratona Blanca variety potato starch exhibits physicochemical and functional characteristics similar to the Andina variety starch but differs in most parameters with commercial potato and corn starches. Potato starches from both native varieties and commercial starch presented the largest granule size higher value in pasting properties, higher crystallinity, higher resistant starch content and higher phosphorus content. On the other hand, corn starch, despite its lower amylose content, presented lower crystallinity, which is associated with its higher digestibility compared to potato starches.
The properties of commercial potato starch were intermediate between Ratona Blanca and Andina potato starches. The latter exhibited superiority in resistant starch content, higher peak viscosity and higher enthalpy. The properties mentioned presented a positive correlation with each other, which could be related to its composition (phosphorus content) and its structure at the molecular level (length and arrangement of amylose and amylopectin chains). These exhibited differential properties can be useful in different fields, such as nutrition and the food industry.
This research was part of the project "Evaluación de la aptitud del almidón de una variedad de papa nativa (Solanum phureja), como ingrediente funcional en la elaboración de productos de panadería con bajo índice glucémico", funded by the Vicerrectoría de Investigación e Interacción Social-VIIS of the Universidad de Nariño. The authors would like to thank the Grupo de Investigación y Desarrollo Agroalimentario-GAIDA for the support and for providing the equipment for the development of this research.
The authors declare that there is no conflict of interest.
Chaves-Morillo, Diana-Melisa: Conceptualization, Methodology, Validation, Formal analysis, investigation, Writing-Original Draft.
Mejía-España, Diego-Fernando: Conceptualization, Formal analysis, Resources, Writing- Review & Editing.