ACID-TREATED STARCHES

Acids such as HCl and H₂SO₄ cause scission of the glucosidic linkages, thereby altering the structure and properties of the native starch. The amorphous regions of the starch granule are more susceptible to acid hydrolysis than the crystalline regions. This review summarizes the current knowledge on: (1) the extent of acid hydrolysis of starches from different botanical origins; (2) the changes in molar mass, crystallinity, viscosity, gel rigidity and gelatinization transition temperatures on acid hydrolysis; (3) the effect of annealing, heat–moisture treatment, high pressure, and amylose-complexed lipids on the rate and extent of acid hydrolysis and; (4) the mechanism of acid hydrolysis in an alcoholic media.     

Effect of Acid Hydrolysis on Starch Structure and Functionality: A Review

Acid hydrolysis is an important chemical modification that can significantly change the structural and functional properties of starch without disrupting its granular morphology.

A deep understanding of the effect of acid hydrolysis on starch structure and functionality is of great importance for starch scientific research and its industrial applications. During acid hydrolysis, amorphous regions are hydrolyzed preferentially, which enhances the crystallinity and double helical content of acid hydrolyzed starch. This review discusses current understanding of the effect of acid hydrolysis on starch structure and functionality. The effects of acid hydrolysis on amylose content, chain length distribution of amylopectin molecules, molecular and crystalline organization (including lamellar structure) and granular morphology are considered. Functional properties discussed include swelling power, gelatinization, retrogradation, pasting, gel texture, and in vitro enzyme digestibility. The paper also highlights some promising applications of acid hydrolyzed starch (starch nanocrystals) in the preparation of biodegradable nanocomposites, bio-hydrogen, and slowly digestible starch-based healthy foods.     

Structural modification of waxy,regular, and high‐amylose maize and hulless barley starches on partial acid hydrolysis and their impact on physicochemical properties and chemical modification

Waxy (WX), regular (RA), and high‐amylose (HA) maize and hulless barley (HB) starches were subjected to partial acid hydrolysis with 1.0 and 2.2 N HCl for 30–240 min. In both starches, the extent of hydrolysis with 1.0 N HCl followed the order: HA>WX>RA, whereas with 2.2 N HCl, the order was: HA>WX>RA (maize) and WX>HA>RA (HB), respectively. The relative crystallinity increased (HA>WX>RA) and the X‐ray pattern remained unchanged, whereas the swelling factor decreased (WX>RA>HA in maize and WX>HA>RA in HB) at both acid concentrations. Starches hydrolyzed with 1.0 N HCl exhibited increased gelatinization temperatures (WX>RA>HA in maize, WX>HA ∼ RA in HB), a narrower gelatinization temperature range (WX>RA>HA in maize, WX>RA ∼ HA in HB) and a decreased gelatinization enthalpy (WX>HA>RA in maize and HB). Acid hydrolysis increased the accessibility of the phosphorylating reagent into the amorphous regions. The extent of phosphorylation was more pronounced (maize>HB) in starches hydrolyzed with 1.0 N HCl for 60–90 min. The bound phosphorus content (BPC) followed the order: HA>WX>RA in maize and HB starches hydrolyzed with 1.0 N HCl for 240 min. In both starches, the extent of cationization was not influenced either by acid concentration or hydrolysis time. In general, acid hydrolysis significantly affected the reactivity of starch towards phosphorylation, where the optimum hydrolysis condition differed with starch source. The results would benefit the starch industry, since the amount of the phosphorylating reagent required for increasing thermal stability and/or freeze‐thaw stability could be decreased substantially, if starches are subjected to partial acid hydrolysis prior to derivatization.     

Tryptophan degradation during heat treatments: Part 2—Degradation of protein-bound tryptophan

The stability of free or protein-bound tryptophan was determined during acid (4 m methane sulfonic acid) or alkaline (4·2 m sodium hydroxide) hydrolysis at 110°C under nitrogen. The influence of time and of glucose, starch or amino acid addition was studied. It was found that hydrolysis with methane sulfonic acid caused tryptophan losses when glucose or starch was present.The thermal degradation of protein-bound tryptophan was studied using either glycyl-l-tryptophyl-glycine or casein. Analysis of tryptophan was carried out after acid or alkaline hydrolysis, through high performance liquid chromatography and UV detection.Heat treatment of tripeptide (9·4 mM, pH 8, 125°C, 3 to 48 h) in the presence of oxygen, air or nitrogen resulted in peptide hydrolysis, with the formation of the corresponding dipeptides and of free tryptophan. After acid or alkaline hydrolysis, tryptophan loss was seen to be higher when the initial heat treatment was performed in the presence of oxygen than in the presence of air.Thermal treatment of 4 or 5% w/v casein solutions (pH 7 or 8) was carried out at 125°C, under oxygen, air or nitrogen. A marked loss of tryptophan was found to occur after 24 h at 125°C when oxygen or air was present. Under nitrogen, protein-bound tryptophan was heat stable, even in the presence of glucose or starch. It is therefore unlikely that the indole ring of protein-bound tryptophan may react with reducing carbohydrates through Maillard-type reactions. Oxidative degradation of protein-bound tryptophan is also unlikely to reach any significant extent during the heat processing of foods, unless catalysts or strong oxidizing agents are present.     

Comparative studies on morphological and crystalline properties of B-type and C-type starches by acid hydrolysis

Comparative studies on acid hydrolysis of B-type Fritillaria starch and C-type Rhizoma Dioscorea and Radix Puerariae starches were carried out using a scanning electron microscope (SEM) and X-ray diffraction (XRD). Fritillaria, Rhizoma Dioscorea and Radix Puerariae starches were hydrolyzed with 2.2 mol/L at 35 °C for 2, 4, 8, 16 and 32 days, respectively. The SEM and XRD results revealed that B-type starch and C-type starch displayed different hydrolysis mechanisms. The acid corrosion started from the exterior surface of B-type starch granules followed by the interior core of starch granules. However, the hydrogen ion primarily attacked the interior of the C-type starch granules and then the exterior of starch granules. B-type starch granule started to crack at the hydrolysis period of 4 days while C-type starch granule was not cracked until the hydrolysis progressed up to 16 days. The crystalline type of B-type starch was not changed with increasing hydrolysis time. However, the crystalline type was gradually changed from C-type to A-type for the Rhizoma Dioscorea and Radix Puerariae starches with increase in the hydrolysis time. This result showed that the B-type polymorphs present in the C-type starch granule was preferentially hydrolyzed during the first stage of hydrolysis.     

Tailoring a New Sizing Agent via Structural Modification of Pregelled Starch Molecules Part 1: Carboxymethylation and Grafting

Pregelled starch (PS) was subjected to acid hydrolysis using phosphoric acid to prepare pregelled starches having different molecular sizes. The degraded pregelled starches were carboxymethylated at different reaction times. The carboxymethyl derivatives were grafted with either methacrylamide (MAam) or methacrylonitrile (MAN) as vinyl monomers using ceric ammonium nitrate (CAN) as initiator. Suitability of the new graft derivatives of pregelled starch as sizing agent of cotton yarns was studied. It is shown by the data that the extent of carboxymethylation, expressed as carboxyl content, increases by increasing the extent of hydrolysis and reaction time. Furthermore, the graft yield, expressed as mmol MAam or MAN monomer/100 g graft copolymer (grafted carboxymethylated pregelled starch or grafted carboxymethylated hydrolyzed pregelled starch) increases with increasing extent of carboxymethylation and degree of hydrolysis and follows the order: MAam > MAN. In addition cotton yarns sized with grafted carboxymethylated hydrolyzed pregelled starch – irrespective of the grafting monomer used – have better mechanical properties (tensile strength, elongation at break, and abrasion resistance) than hydrolyzed pregelled starches, carboxymethylated pregelled starch and carboxymethylated hydrolyzed pregelled starches.     

Nonthermal starch hydrolysis using ultra high pressure: I. Effects of acids and starch concentrations

Corn starches with 2 mol/l hydrochloric acid (HCl), 2 mol/l sulfuric acid (H₂SO₄) and 2 mol/l oxalic acid (C₂H₂O₄) were pressurized at 600 MPa for 30 min. Corn starch with C₂H₂O₄ formed a gel after ultra-high-pressure (UHP) treatment. Corn starch with HCl showed partial disintegration but starch with H₂SO₄ maintained its shape. Corn starch with HCl showed higher (0.42-0.47) degree of hydrolysis compared to starch with C₂H₂O₄ (about 0.14) and H₂SO₄ (0.13-0.14) regardless of increasing starch concentration up to 20 g/100 g sample. Main component of starch hydrolysate was maltose for HCl and oligosaccharides for H₂SO₄ and C₂H₂O₄. Crystallinity of starch with HCl decreased with decreasing starch concentration as observed by both differential scanning calorimetry (DSC) and X-ray diffraction. Therefore, UHP can be used for nonthermal starch hydrolysis and HCl would be a good catalyst for UHP starch hydrolysis compared to H₂SO₄ and C₂H₂O₄. This work provides a potential of nonthermal UHP processing for new starch hydrolysis method.     

Characteristics of L-lactic Acid Production byRhizopus oryzae mutant RL6041

A high-yield mutant strain Rhizopus oryzae RL6041 induced by ions implantation was used in the present study. L (+)-lactic acid was generated by RL6041 grown on liquefied corn starch as a substrate. With optimal conditions (Liquefied corn starch 150g/L, (NH₄)₂SO₄ 2.0g/L, MgSO₄·7H₂O 1.0g/L, ZnSO₄·7H₂O 2g/L, KH₂PO₄ 0.2g/L, CaCO₃ 8%, medium size 20/250Ml, seed age 6h, fermentation temperature 38° C), the yield of L (+)-lactic acid in shake-flask reached 133∼136g/L after 36h, indicating that the conversion rate was as high as 88%∼91%, and the productivity was 3.75g/L·h. There was almost a 70% increase in lactic acid production compared with the original strain RE3303.     

The structure of C-type Rhizoma Dioscorea starch granule revealed by acid hydrolysis method

Scanning electron microscope (SEM), X-ray powder diffraction (XRD) and cross polarisation/magic-angle spinning (CP/MAS) ¹³C nuclear magic resonance (NMR) have been used for the structural characterisation of C-type starch granule during acid hydrolysis. SEM shows that the amorphous areas mainly locate the core part of C-type starch granules, while the crystalline areas mainly exist in the peripheral region of starch granules. XRD analysis reveals that the B-type polymorph present in the C-type starch granule are preferentially degraded or degraded faster than the A-type polymorph. NMR spectra confirm that the amorphous regions in the starch granules are firstly hydrolysed and could be hydrolysed completely as long as the hydrolysis time is sufficient. After 40 days of hydrolysis, the acid-modified starch shows typical A-type characteristics upon analysis of the XRD pattern or the ¹³C CP/MAS NMR spectra.     

In vitro Effects of Phytic Acid and Polyphenols on Starch Digestion and Fiber Degradation

The effect of phytic acid and polyphenols on the rate and extent of starch digestion as well as on fiber degradation was studied in vitro. Addition of phytic acid only had negligible influence on the enzyme activity of the amylases tested. In contrast, enzymes concerned with starch hydrolysis in the digestive channel (α-amylase, amyloglucosidase/maltase) were inhibited by tannic acid, and to some extent also by catechin. Furthermore, tannic acid reduced the total recovery of starch during enzymic starch analysis. The activity of cellulases and hemicellulases was not affected by phytic acid or catechin. However, the degradation of cellulose powder was inhibited by tannic acid, whereas no inhibition could be observed with carboxymethyl-cellulose as substrate.     

Effects of fatty acid and emulsifier on the complex formation and in vitro digestibility of gelatinized potato starch

The effects of fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with varying chain length in their acyl chains on the extent of complex formation (complex index) and in vitro enzymatic digestibility of gelatinized potato starch were investigated. The complex index increased with increase in the concentration of the ligands (fatty acid, monoacylglycerol, and polyglycerol fatty acid ester), with the plateau in the complex index value depending on the type of ligands. In comparison of complex index among fatty acid-samples, the complex index maximum increased as the chain length increased up to octanoic acid and then decreased. In comparison of complex index among fatty acid-, monoacylglycerol-, and polyglycerol fatty acid ester-samples at each acyl chain, the complex index maximum followed the order polyglycerol fatty acid ester > monoacylglycerol > fatty acid. Fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with long acyl chains greatly reduced the enzymatic hydrolysis of starch. Polyglycerol fatty acid ester with palmitic acid chains was the strongest inhibitor of starch hydrolysis, suggesting that further complex formation may occur during the hydrolysis of gelatinized starch (enzyme-annealing).     

酸解时间对大米淀粉结构性质的影响

以4种不同直链淀粉含量的大米淀粉(0%的优糯3号、10.90%的稻花灿、21.03%的聚两优、28.46%的华优香占)为原料,酸解处理不同时间,以酸解大米淀粉的酸解率、颗粒形貌、结晶性质、溶解度的变化为指标衡量不同酸解时间对大米淀粉结构及性质的影响。结果表明,不同直链淀粉含量的大米淀粉具有不同的耐酸性,酸解时间对不同直链淀粉含量大米淀粉的结构和性质有着不同的影响。大米淀粉酸解率与直链淀粉含量成反比,优糯3号为50%而华优香占仅为30%;所有淀粉颗粒在酸解后均产生一定程度的破碎,偏光十字变形直至消失,酸解相同时间,直链淀粉含量高的大米淀粉破碎率低;酸解未改变淀粉的晶型,仍为A晶型;随着酸解时间的延长相对结晶度增加;淀粉的溶解度随着酸解时间的增加而增大。     

Effect of acid hydrolysis on rheological and thermal characteristics of lentil starch slurry

A comparative rheological and thermal study was carried out between acid hydrolyzed and unhydrolyzed (control) lentil starch dispersions (25-33.3 g starch per 100 g water) as function of temperature. After acid hydrolysis, the peak gelatinization temperature (T_p) shifted to higher temperature than the corresponding starch without hydrolysis whereas the gelatinization enthalpy remained unaffected by hydrolysis. The starch gelatinization kinetics was evaluated by a non-isothermal technique as function of elastic modulus (G′) and G′ vs. time (t) data up to the gelatinization peak value was considered for rate estimation. A 2nd-order reaction kinetics described well the starch gelatinization process and the process activation energy was ranged between 241 and 434 kJ/mol. Acid hydrolysis strongly affected the rheological properties by lowering gel strength compared to unhydrolyzed starch. The creep analysis further revealed that starch gel was significantly affected by hydrolysis and exhibited less resistant to the stress. A 4-parameters Burgers model well-described creep curves and supported oscillatory rheological data.     

Degradability of Different Phosphorylated Starches and Thermoplastic Films Prepared from Corn Starch Phosphomonoesters

Different starch types (corn, rice, potato, corn amylose and corn amylopectin) were phosphorylated to varying degrees of substitution (DS) and tested both for acid hydrolysis during 3 h in a boiling bath and for enzymatic hydrolysis with a thermostable bacterial α‐amylase (Bacillus licheniformis) for 30 min at 95 °C. Generally, phosphorylated starches showed a reduced degree of acid hydrolysis during the entire time of hydrolysis (3 h) as well as reduced susceptibility to α‐amyIase hydrolysis. The enzyme action was inhibited by the presence of phosphate groups in the modified starch molecules and the extent of inhibition increased with increasing degree of phosphate substitution, regardless of the starch type. Thermoplastic films were fabricated by blending modified corn starches of different DS with polyacrylate, urea and water at a ratio of 4:5:1:50, heating for 30 min at 95 °C before casting and allowing to cool, stand and dry at room temperature. The plastic films prepared from phosphorylated corn starch showed both higher disintegration rate and a greater degradability by thermostable bacterial α‐amylase than the ones prepared from non‐phosphorylated starch. These new acquired properties can meet the increasing demand for biodegradable disposable plastic bags.     

酶法、酸法制备碎米多孔淀粉工艺研究及其比较

以碎米为原料,分别采用酶法、酸法制备多孔淀粉,通过单因素和正交试验,得到两种方法制备碎米多孔淀粉的最佳工艺条件,酶法制备碎米多孔淀粉最佳工艺条件为液料比4:1(mL/g)、加酶量23.0U/g、pH7.0、酶解温度60℃、酶解时间7h;酸法制备碎米多孔淀粉最佳工艺条件为液料比4:1(mL/g)、盐酸浓度0.4mol/L、酸解温度35℃、酸解时间6h。经比较酶法比酸法制得的多孔淀粉吸油率高13.3%。运用扫描电子显微镜对多孔淀粉的颗粒形态进行比较,结果表明酶法比酸法制得的多孔淀粉出孔率高、孔径大、孔穴深。     

New insights into loss of swelling power and pasting profiles of acid hydrolyzed starch granules

The effect of acid hydrolysis on the swelling power of pea starch granules was studied by field emission SEM (FE‐SEM). The swelling power of the native starch granules (g water absorbed/g dry starch) was 13, and this decreased to less than 2 after 1 day of acid hydrolysis. The proportion of the starch that was soluble in hot water increased from 15% for native starch to 75% after 1 day of hydrolysis. The swelling power of the starch decreased further, and solubility increased, with more extended hydrolysis. The decrease in swelling power and increase in solubility were attributed mainly to the disruption of side chains of amylopectin. Observations with FE‐SEM indicated that starch granules were still able to melt and coalesce after 1 day of acid hydrolysis, but after 2 days solubilization of starch chains occurred predominantly rather than swelling when the granules were heated in excess water. The intactness of amylopectin is proposed to play a crucial role in the swelling power of starch granules and in the structure of granule ghosts.     

Aerobic Biodegradation of Extruded Polymer Blends with Native Starch as Major Component

The aerobic biodegradation of extruded blends containing native starch and an acetylated compound (starch or cellulose) was studied with the Bacillus amyloliquefaciens strain and also with the Biolen mixture known for its amylolytic activity. In the presented experiments, the rate of biodegradation is related to the percentage of acetylated compound in the blend. In fact, if the blend hydrolysis is facilitated by the amorphous state of the substrate, the inhibitory action of the acetyl group content is the major factor responsible of the weak hydrolysis. For instance, the conversion of the carbon material into CO₂ decreases strongly from 39% (native starch alone) to 7% (equimolar blend of starch and acetylated compound). All the other parameters used to estimate the hydrolysis extent (as the production of reducing sugars or acetic acid release) lead to the same conclusion.     

The Reactivity of Porcine Pancreatic alpha-Amylase Towards Native,Defatted and Heat-moisture Treated Potato Starches Before and After Hydroxypropylation

Potato starch was defatted (hot 75% n-propanol) and heat-moisture treated (100°C, 30% moisture) for various time intervals. The results showed that the above treatments increased the susceptibility of potato starch granules (heat-moisture treated > defatted) towards hydrolysis by porcine pancreatic α-amylase. These differences can be accounted for by the structural changes that occur within the amorphous and crystalline regions of the starch granule during defatting and heat-moisture treatment. Native, defatted (7 h) and heat-moisture treated (100°C, 30% moisture, 16 h) potato starches were hydroxypropylated (to different levels of molar substitution [MS]) with propylene oxide (2 → 20 %). The results showed that the alkaline reagents (NaOH and Na₂SO₄) used during hydroxypropylation increased the susceptibility of the above starches (native > defatted > heat-moisture treated) towards hydrolysis by α-amylase. Addition of propylene oxide to alkali treated starches, further enhanced their susceptibility, towards α-amylase. However, granule susceptibility towards α-amylase did not increase exponentially with increase in MS. The extent of hydrolysis began to decrease at MS levels of 0.29 (native), 0.28 (heat-moisture treated) and 0,26 (defatted).     

Physicochemical,thermal, and rheological properties of acid-hydrolyzed sago (Metroxylon sagu) starch

The effects of acid hydrolysis on physicochemical and rheological properties of sago starch were investigated. Sago starch was hydrolyzed in hydrochloric acid at 50 °C for 6, 12, 18, and 24 h. The molecular weight distribution, physicochemical, thermal, and rheological properties of acid-hydrolyzed sago starch (AHS) were determined. After 24 h of hydrolysis, molecular weight of amylopectin and amylose were decreased to 3.57 × 10⁵ and 6.5 × 10⁴ g/mol, respectively. Differential scanning calorimetry studies showed that the gelatinization temperature and enthalpy of AHS increased with increasing degree of hydrolysis. Hydrolyzed sago starch containing low molecular weight fractions exhibited cold water solubility up to 100%. Setting temperature of AHS decreased with increasing hydrolysis time but amylose content and gel strength increased in the first 12 h of acid hydrolysis but decreased with extended hydrolysis time. Hydrolyzed sago starch in concentrations lower than 8 g starch per 100 g water was cold water soluble and could be used to modify properties of starch for specific applications such as yogurt and concentrated milk processing.     

Structural and physicochemical characterization of RS prepared using hydrolysis and heat treatments of chickpea starch

The aim of this study was to evaluate the production and the structural and physicochemical properties of RS obtained by molecular mass reduction (enzyme or acid) and hydrothermal treatment of chickpea starch. Native and gelatinized starch were submitted to acid (2 M HCl for 2.5 h) or enzymatic hydrolysis (pullulanase, 40 U/g per 10 h), autoclaved (121°C/30 min), stored under refrigeration (4°C/24 h), and lyophilized. The hydrolysis of starch increased the RS content from 16% to values between 20 and 32%, and the enzymatic treatment of the gelatinized starch was the most efficient. RS showed an increase in water absorption and water solubility indexes due to hydrolytic and thermal process. The processes for obtaining RS changed the crystallinity pattern from C to B. Hydrolysis treatments caused an increase in relative crystallinity due to the greater retrogradation caused by the reduction in MW. RS obtained from hydrolysis showed a reduction in viscosity, indicating the rupture of molecules. The viscosity seemed to be inversely proportional to the RS content in the sample.