Effect of Pretreatment of Fresh Amorphophallus paeoniifolius on Physicocochemical Properties of Scratch

V.Sunitha Rani, Jancy K.John, S.N.Moorthy and K.C.M.Raja, Trivandrum (India)

Introduction

Edible tubers of tropical root crops viz. Dioscorea, Colocassia, Xanthosoma, Amorphophallus sp. etc. form and important food source [1, 2]. Although the major organic constituent of all the above crops is starch, accounting for 10-35% on fresh weight basis [3], extraction of starch does not often bring adequate yield. This is mainly due to the fact that tubers, unlike cassava, often contains constituents other than starch that interferes with the process of starch extraction. Similar problems arise also during extraction of starch from cereals. Hence, subjecting root/cereal crops to physico-chemical pretreatments is often practiced to enhance the starch yield [4]. Jawad and Lorenz [5] reported that steeping wheat of poor baking quality increased the starch yield as well as susceptibility to ά-amylase action. Hoover and Hadzijeve [6] had used sodium bisulphate during homogenization and extraction of starch from potato tubers, Lorenz and Kulp [7] are of the opinion that organization of starch is not fixed and could get altered by the conditions adopted for isolation. Addition of 0.01% sulphite enables release of polysaccharides reflecting on the swelling volume [8] of starch. Amorphophallus paeoniifolius being an important food crop grown in different parts of the country, and its starch having characteristics properties, extraction of starch in good yield without affecting the quality has great potential for better utilization [9,10]. Studies were, therefore, carried out to examine in detail, the effect of pretreating fresh tubers with a few selected chemicals on the yield and physicochemical quality of starch obtained.

Materials and Methods

1. Raw Materials

   Fresh root of Amorphophallus paeoniifolius were procured from local market and they had a moisture content in the range of 75-76%.

2. Bacterial ά-amylase

   Bacterial ά-amylase having an activity of 222.5 units/mg solid (Sigma USA) was used for the study.

3. Chemicals

   All the chemicals used for the experiments were purchased from Indian manufactures and they were of analytical reagent grade.

Experimental

1. Extraction of starch

   Extraction of starch from the tubers was done as per the procedure given in the flow chart (Fig 1 is given below 3.2.4)

2. Analytical

   1. Starch yield

      Total starch yield was determined gravimetrically.

   2. Moisture

      Moisture content in the starch samples was determined by standard air-oven method^[11].

   3. Amylose contents

      Apparent, true and water soluble amylase contents, were determined using reported standard methods ^{[12, 13]}

   4. Intrisnsic viscosity

      Relative viscosity (η r) of starch samples was determined at 30⁰C in alkaline solution using Ostwald Viscometer based on the method of Meyers and Smith ^[14]. From the above value intrinsic viscosity ηi was calculated from the following equation ηi = 2.303 log ηr/ concentration
      Fresh tuber (250g)

      
      

      Sliced to 3 cm thickness

      
      

      Ground with 150ml aqueous solutions/Water

      
      

      Mixed with excess of aqueous solution/ water

      
      

      Settled for one h

      
      

      Filtered through sieve of 180 mesh size

      Residue discarded

      
      

      
      

      Washed with 1 L H₂O

      
      

      Stored under a layer of toluene

      
      

      Decanted, washed with 1 L H₂O

      
      

      Kept for 3 h

      
      

      Decanted and filtered

      Supernant discarded

      
      

      
      

      Wet starch dried to 10% moisture

      Fig. 1. Flow sheet for extraction of starch from Amorphophallus paeoniiflius.

   5. Swelling volume and solubility

      Swelling volume and solubility of starch samples were determined essentially by adopting the method of Schoch [15] as follows :
      
      100 mg each of the sample was accurately weighed and transferred to 50 ml conical flask. After adding 10 ml distilled water, the flask was placed in a boiling water bath for 10 min till it gave a translucent suspension. Subsequently, the solution was centrifuged and volume of the residue was noted after centrifugation. 2.0 ml aliquot from the filtrate was pipetted and transferred to a pre-weighed petry-dish and dried at 70°C by keeping in an oven. The dish was cooled and weighed. From the value obtained percentage solubility was calculated.

   6. X-ray diffraction studies

      X-ray diffraction pattern of starch granules was examined on a Phillips X-ray diffractometer using Cu kα radiation.

3. Starch Yield

   The pattern of starch yield obtained from fresh roots of Amorphophallus paeoniifolius, pretreated with aqueous solutions of SHMP, KMS, NaCL, NH₄OH and GMS is presented in Fig.2. The above pattern suggests that treatment of fresh roots with SHMP below 2% does not affect starch yield adversely, but above 2% level there was a progressive decline in the yield of starch obtained. Pretreatment of fresh tubers with KMS, on the other hand, showed a tendency to reduce the starch yield consistently. Treatment of fresh roots with either GMS or NH₄OH did not display any predictable and consistent pattern regarding the yield of starch obtained. It is presumed that the above tendency for lowering the starch yield noticed in the case of samples prepared from fresh roots pretreated with KMS could be due to degradation in the macromolecule. The extent of starch purity estimated as total carbohydrate content and expressed as starch content (Fig 3) did not show any reduction in the case of samples prepared from either SHMP or KMS treated roots. There was, however, found to be a reduction in starch purity in the case of samples prepared from GMS or NH₄OH treated samples above 0.025% and 1% respectively. From the results, it is to be inferred that treatment of fresh roots with SHMP below 2% concentration is preferable to others as far as starch yield is concerned.

4. Swelling volume and solubility

   Results of the experiments conducted on swelling and solubility of starch samples prepared from fresh s well as chemically pretreated roots are presented in Table 1. Table 1. Swelling volume and solubility of starch samples prepared from Amorphophallus paeoniifolius.

   Exptl.No.	Sample	Swellingvolume (ml)	Solubility(%)
   I	Starchcontrol	27.7	23.0
   II	Starchsamples from pretreated roots SHMP treated
   	1%SHMP treated	24.5	18.5
   	2%SHMP treated	26.0	18.5
   	3%SHMP treated	25.5	16.5
   	4%SHMP treated	24.5	18.5
   	5%SHMP treated	24.0	18.8
   	NaCltreated
   	1%NaCl treated	27.5	18.1
   	2%NaCl treated	25.5	18.6
   	3%NaCl treated	24.5	ND
   	4%NaCl treated	27.5	14.5
   	5%NaCl treated	28.0	8.9
   	NH4OH treated
   	1%NH4OH treated	23.5	26.8
   	2%NH4OH treated	23.0	32.5
   	3%NH4OH treated	24.0	28.4
   	4%NH4OH treated	25.0	24.4
   	5%NH4OH treated	25.0	24.4
   	KMStreated
   	1%KMS treated	26.0	22.2
   	2%KMS treated	28.0	30.6
   	3%KMS treated	27.0	29.2
   	4%KMS treated	28.0	28.0
   	5%KMS treated	25.0	29.9
   	GMStreated
   	0.025%GMS treated	22.5	32.9
   	0.050%GMS treated	22.5	19.5
   	0.075%GMS treated	19.5	10.25
   	0.100%GMS treated	ND	ND
   	0.125%GMS treated	20.5	24.0

   The average values for swelling volume (ml) and solubility (%) of starch samples obtained from fresh roots directly extracted with distilled water were 27.7 and 23.0, respectively. Pretreatment of fresh roots with chemicals changed the swelling and solubility pattern to a noticeable level in a distinct manner. Treatment of fresh roots with different concentrations of SHMP showed a tendency to lower the swelling volume and solubility of the starch samples. A similar trend in the values of swelling volume was noticed in the case of starch samples pretreated with 1-5% NaCL. In the above case, highest reduction in swelling volume was noticed in samples prepared 3% NaCL. Increased solubility was observed in the starch samples prepared from roots treated with glycerylmonostearate at a level of 0.025% and also from those pretreated with KMS. Patterson et al. [16] have pointed out that presence of salts such as NaCL and sulphite at higher temperatures, viz 95°C enables the release of polysaccharides and in the case of potato and cassava starches, the measured volume showed a marked reduction. It is possible that contact of fresh roots with higher concentrations of salt solution (1-5%) at room temperature during soaking and subsequent extraction could bring structural changes in the polysaccharide which may result in reducing the swelling volume of starch as noticed in the present study. The observed reduction in swelling volumes in samples prepared from the roots pretreated with SHMP and NaCL could be attributed either to breakdown of starch or due to inhibition of starch swelling by physical interaction of the chemical with the starch. Treatment of fresh roots with NH₄OH or KMS could lead to breakdown of starch by virtue of alkaline or acidic environment caused during treatment. Hashim et al. [18] observed a similar effect of Na₂S₂O₃ in reducing swelling volume of starch at lower concentrations.

5. Amylose blue value

   Results of the analysis done for true, apparent and water-soluble amylase, measured as blue values are presented in Table 2. Deffating of starch sample with methanol increased the amylase blue in all the samples. Pretreatment of fresh roots with chemicals showed a tendency to reduce the water soluble amylase content. The above decrease in soluble amylase could be attributed to the possible complexation of part of the amylase fragments with the chemicals used for pretreatment. Similar results have been reported from the earlier studies on the extraction of different starches with ammonia solution [10] and also in the treatment of cassava starch with different surfactants [17, 18].

6. ἀ-Amylase susceptibility

   Pattern of ἀ-amylase susceptibility of starch sample obtained from untreated and chemically pretreated root samples are presented in Fig.4. In the case of control and also starch samples prepared from roots treated with 1% NH4OH and KMS, the highest activity was noticed during the initial 5 min of incubation. Subsequently, the activity was found to progress at a uniform pace up to 15 min. Beyond 15 min, samples showed reduced ἀ-amalyse activity. In the case of starch samples pretreated with NaCL, the highest susceptibility was seen at 10 min of incubation, beyond which the enzyme activity declined. For starch samples treated with 0.075% GMS, the highest activity was noticed at 15 min incubation. The general observation was that after incubation for 15 min at 70°C, all the samples showed more or similar tendency of declining enzyme susceptibility. There was a time lag in attaining the highest activity in the case of starch samples prepared from roots pretreated with NaCL and GMS. The above phenomenon suggests some structural changes in starch samples resulting in partial shielding of ? 1-4 cities available for ἀ-amylase attack, which is to be confirmed.

   Exptl.No.	Sample	Blue value
   		True Amylase	Apparent amylase	Soluble amylase
   1	Starch Control	0.01416	0.01379	0.0096
   2	Starch samples from treated roots
   	SHMP treated
   	1% SHMP treated	0.1436	0.1417	0.01144
   	2% SHMP treated	0.01400	0.01428	0.01315
   	3% SHMP treated	0.01430	0.01412	0.01215
   	4% SHMP treated	0.01440	0.01431	0.01301
   	5% SHMP treated	0.01500	0.01468	0.01026
   	NaCl treated
   	1% NaCl treated	0.01491	0.01412	0.0089
   	2% NaCl treated	0.01495	0.01467	0.0091
   	3% NaCl treated	0.01455	0.01468	0.0095
   	4% NaCl treated	0.01477	0.01468	0.0085
   	5% NaCl treated	0.001500	0.01468	0.0089
   	KMS treated
   	1% KMS treated	0.01491	0.01460	0.0084
   	2% KMS treated	0.01530	0.01480	0.0089
   	3% KMS treated	0.01533	0.01519	0.0094
   	4% KMS treated	0.01443	0.01417	0.00084
   	5% KMS treated	ND	ND	ND
   	GMS treated
   	0.025% GMS treated	0.01275	0.01232	0.00692
   	0.050% GMS treated	0.01181	0.01160	0.00675
   	0.075% GMS treated	0.01171	0.01032	0.00617
   	0.100% GMS treated	ND	ND	ND
   	0.125% GMS treated	ND	ND	ND

7. Intrinsic Viscosity

   As shown in Table 3 intrinsic viscosity of starch samples from Amorphophallus roots was of the order of 1.8301. It could be generally noticed that starch samples prepared from fresh roots pretreated with NaCL in the range of 1-5% raised the intrinsic viscosity by a range of 9.5 to 15.62%. A similar observation although to a less extent could be noticed in the case of starch samples obtained from SHMP treated samples also.

8. X-Ray Diffraction

   A comparison of specific data on'd' spacing, angle (2?) and peak intensity (Io/Imax) of the experimental samples with reported data [19] for standard 'A', 'B' and 'C' types reveals that X-ray diffraction pattern of starches isolated from control as well as chemically pretreated samples were generally identical and resembled with that of 'A' type than 'B' OR 'C' type. A similar observation has been made earlier by Moorthy et al. [10]. From the data as presented in Table 4, it could be noticed that starches prepared from chemically pretreated root samples did not show any significant change. However, there was a noticeable shift in the peaks with respect to both, angle (2?) as well as intensity (Io/Imax), indicating a partial change in crystalline phases. Table 3. Intrinsic viscosity of starch samples from Amorphophallus paeoniifolius.

   Exptl.No.	Sample	Intrinstic Viscosity (%)
   1	Starch Control	1.8301
   2	Starch samples from treated roots
   	SHMP treated
   	1%SHMP treated	1.9714
   	2%SHMP treated	2.124
   	3% SHMP treated	1.9465
   	4% SHMP treated	2.0584
   	5% SHMP treated	2.0833
   	NaCl treated
   	1% NaCl treated	2.0770
   	2% NaCl treated	2.1130
   	3% NaCl treated	2.1160
   	4% NaCl treated	2.0040
   	5% NaCl treated	2.2000
   	NH4OH treated
   	1% NH40H treated	1.9490
   	2% NH40H treated	1.9050
   	3% NH40H treated	1.4980
   	4% NH40H treated	1.6320
   	5% NH40H treated	1.5500
   	KMS treated
   	1% KMS treated	1.9280
   	2% KMS treated	1.7530
   	3% KMS treated	1.9640
   	4% KMS treated	1.0280
   	5% KMS treated	2.1720
   	GMS treated
   	1% KMS treated	1.3060
   	2% GMS treated	2.0040
   	3% GMS treated	2.1360
   	4% GMS treated	ND
   	5% GMS treated	ND

Conclusion

Studies on the effect of pretreating fresh roots of Amor-phophallus paeoniifolius using a few selected chemicals, viz. SHMP, KMS, NaCL, GMS and NH4OH were carried out in order to assess the changes in starch yield, starch purity (%) and properties such as amylase blue value, intrinsic viscosity, swelling volume and solubility at 95°C. Changes in ά-amylase susceptibility and X-ray diffraction pattern were also looked into. The impact of pretreatment of fresh roots was more pronounced with respect to swelling volume and solubility and to some extent, ά-amylase susceptibility. No major change in X-ray diffraction pattern or total and apparent amylase blue value could be noticed.

Bibliography

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Addresses of authors: Miss V. Sunitha Rani, Senior Research Fellow, Technology Division, Central Tuber Crops Research Institute (CTCRI), Sreekaryam, Trivandrum Kerala-695 017; Ms Jansy K. John, Senior Research Fellow, BCP & WWT Division, Regional Research Laboratory (RRL), Trivandrum, Kerala 695 019; Dr. S.N. Moorthy, Scientist (CTCRI), Trivandrum 695 014; Dr. K.C.M. Raja*, Scientist * Corresponding author. (Received: May 29, 1997).