The study investigated the effects of heat-moisture treatment (HMT) using an oven and autoclave on the properties of purple yam flour. HMT increased resistant starch and decreased rapidly digestible starch, with autoclaving having a greater impact due to higher heat transfer. Autoclaving transformed the starch crystalline structure from B-type to the more crystalline and resistant A-type, improving the flour's potential as a prebiotic.

1. BIOCHEM-691
Presented by
Shreya Mandal
11733
PhD 2nd year
Division of Biochemistry
2021-22

2. INTRODUCTION
Starch provides people with metabolic energy and nutrients
Long-term use of high-glycemic meals increases the risk of chronic diseases like obesity and type 2
diabetes
Retrogradation, syneresis, inability to sustain shear stress, and its unstable nature at different
temperatures and pH environments limit the applicability of starch in its natural state
Starch must be modified in order to improve its food and industrial applications
Autoclaving-retrogradation, complexation with other food-derived components such as protein,
polyphenol, and hydrophobic antioxidant, have been used to reduce starch digestibility
Hydrothermal treatments, such as annealing and heat-moisture treatment, are also beneficial in
modulating starch hierarchical structures and lowering RDS content.
α-amylases, β-amylases, transglucosidases, pullulanases, isoamylases, and amylosucrases, have
been widely used in the enzymatic approach to retard retrogradation and boost starch enzymatic
resistance

3. INTRODUCTION
The FAO/WHO/IAEA Joint Expert Committee on Food Irradiation has unconditionally cleared foods
irradiated up to 10 kGy as safe for human consumption since irradiated food is wholesome and
nutritionally adequate.
The effects of gamma irradiation on the physico-chemical, thermal, functional, and microbiological
properties of various flours have been studied by a number of researchers.
Dioscorea alata commonly known as purple yam is actually a species of yam, a tuberous root
vegetable

4. Materials and Methods
• Fresh purple yam tubers (D. alata Purpurea)
• Determination of proximate composition (moisture, ash, protein, and fat) was by using AOAC 2005
methods
• Amylose content was according to Tiamiyu et al. (2017)
• Preparation of purple yam flour: 5 cm thick cut was rinsed with tap water, then immersed in 0.5 percent
acetic acid solution for a few minutes then kept for steaming for 5 minutes, then dried at 50°C, milled, and
sieved in 210 μm
• SC ( g / g ) = Weight of the wet mass sediment /Weight of sample (g dry basis)
• Solubility (%) = [Weight of dry supernatant /Weight of sample (g dry basis)] × 100
• Digestibility test was performed based on the method by Englyst et al., 1992

5. Materials and Methods
The samples with water content variations of 15%, 22% and 30% using oven method
(Memmert UN 55 53L; 5◦C above ambient up to ± 300 ̊C) at 100 ̊C and 120 ̊C were
denoted as OHMT1₁₅; OHMT1₂₂, OHMT1₃₀; OHMT2₁₅; and OHMT2₂₂; OHMT2₃₀,
respectively
The HMT was also repeated using the autoclave (Daihan WACS-1045-1.2 Kgf/cmᶾ at
120 ̊C) thrice at 100 ̊C and 120 ̊C for 1 h. Therefore the samples were abbreviated as
AHMT1₁₅; AHMT1₂₂, AHMT1₃₀; AHMT2₁₅; and AHMT2₂₂ ;AHMT2₃₀, respectively
Fourier transforms infrared spectroscopy (FT-IR) analysis
X-ray diffraction (XRD) analysis : RC (%) = (AC/ AC + Aa) × 100

6. Results and discussion
Chemical composition of purple yam flour
purple yam flour’s chemical components were estimated to reduce swelling power,
solubility, digestibility, and other characteristics

7. Results and discussion
Swelling capacity and solubility of native and HMT
purple yam flours
AHMT greatly
influenced both
characteristics
compared to OHMT
The flour solubility also
decreased to 12.87% and
that of AHMT to 16.41%
OHMT swelling power
decreased around 12.42
(g/g), and more drastically
at 16.89 (g/g) in AHMT
The increase in
solubility, temperature
and moisture content
(oven and autoclave)
was reported in
Dioscorea alata starch
(Tiamiyu et al., 2017)

8. Results and discussion
Effect of HMT three cycles on digestibility properties of
purple yam flour
I. On both treatments, the
RDS reduced to 9–17% and
11–17%, correspondingly
II. SDS and RS of OHMT and
AHMT modified flours
increased to 4–16% and 4–
15%, as well as 7–14% and
5–18% respectively
compared to native

9. Illustration of rearrangement of polymer chain
under heating, cooling, and storage condition

10. Effect of HMT three cycles on digestibility properties of
purple yam flour
• Temperature, moisture content, heating time and starch source are the main factors affecting crystallinity and
starch digestion.
• RS is polymer structures’ rearrangement product that is more ordered and not covered by amylase’s active site
to hydrolyze glycosidic bonds (α-1,4 amylose and α-1,6 amylopectin)
• SDS is a very rigid amorphous area that can be derived from retrograde products due to cooling and crystalline
regions’ partly disturbance
• Increasing the heat and moisture level also increased the polymer chain interaction’s mobility, hence the
amorphous areas’ crystalline arrangement occurred
• Changes in crystallinity pattern (B-type to A-type) led to more resistant starch against amylase
• The A-type is stronger because the double helix arrangement in the crystalline structure is directly connected
by hydrogen bond
• While B-type is mainly linked by hydrate water bridges and inadequately by direct hydrogen bonding
• RS3 is retrograded in nature due to hydrogen bonds’ reassociation between short chain amylose formed after
the autoclave process and cooling at low temperature. The process will have an impact on the formation of
new small crystalline areas in the starch granules

11. Results and discussion
Absorbance ratio of native purple yam flour and modified HMT
Fourier Transform-Infra Red
spectra of native and HMT flour
using (a) oven, and (b) autoclave
 Absorption bands at 1047 cm− 1 /1022 cm− 1 are associated with starch grains’
crystalline and amorphous domains, respectively and the ratio (1047 cm− 1
/1022 cm− 1 ) is used to indicate starch granules’ degree of crystallinity
 The increased 1047 cm− 1/1022 cm− 1 ratio is related to the increased
structural organization

12. Results and discussion
Peak intensity and crystallinity of native and HMT purple yam flours
X-ray diffraction pattern of
native and HMT flour using (a)
oven, and (b) autoclave
Samples
subjected to
autoclave HMT
had higher
relative
crystallinity
compared to oven
 OHMT222 and AHMT222 had high crystallinity of 50.90% and 51.35%,
respectively

13. Peak intensity and crystallinity of native and
HMT purple yam flours
• The increase was due to structural rearrangement in starch granule crystals’
field, where moisture content and thermal energy during the HMT process led
to double helices displacement, which initiated better crystals formation
• The decreased X-ray peak intensity showed the loss of crystal arrangement. This
was probably due to the damaged hydrogen bond, which caused adjacent
double helix displacement and imperfect parallel rearrangement in orientation
• HMT modified purple yam flour increased peak intensity was due to 36 water
molecules’ evaporation in the central channel causing the starch granules to be
more crystalline

14. CONCLUSION
Heat moisture treatment (HMT) in three cycles utilising an oven (OHMT) and autoclave (AHMT)
(100°C and 120°C; moisture levels: 15%, 22%, and 30%) successfully improved the physical,
chemical, and digestibility properties of Purple yam flour
All of the treatments raised SDS (4–16%) and RS (7–13% and 5–18%), respectively, and altered the
X-ray diffraction pattern and intensity
The starch B-type was transformed to A by OHMT2 and AHMT2 ₁₅, ₂₂, ₃₀ but only in the sample with
30% moisture content by OHMT1 and AHMT1
OHTM and AHMT both improved relative crystallinity by 6–19% and 10–20%, respectively
We came to the conclusion that AHMT had a greater impact on all physicochemical and digestibility
factors than OHMT

15. ADVANTAGES
Despite having a negative impact on the starch granules' crystallographic patterns, HMT was
found to have a good impact on the nutritional (resistant starch) and functional aspects of
the modified starches
As a result of the HMT modification of starch, better grade starch is easily available for
usage and application by food processors and businesses
RS3 is also relatively heat resistant compared to the other RS types, therefore it is stable
during food processing
It can be fermented by probiotic bacteria leading to short-chain fatty acid (SCFA) so It
modulates probiotic bacterial growth, stimulates the immune system, inhibits pathogens in
the intestine and reduces constipation
The treated purple yam flour can be used as a prebiotic carbohydrates source based on the
findings

16. SUMMARY
 The physicochemical properties of purple yam flour showed significant changes after HMT
treatment
 The difference of characteristic is due to the strength of heat transfer in the two thermal sources
 Heat transfer in the autoclave is much greater than in the oven, which produces more
homogeneous exposure times to all parts of the sample
 Modification of starch using autoclave can be achieved quickly because of the high heat transfer
coefficient, which impacts the mobility of the starch polymer chains
 The higher heat transfer in the autoclave can force the evaporation of 36 water molecules in a
double helix (type B) resulting in a rearrangement of the polymer structure into a more
crystalline type A. The arrangement will ultimately have an impact on swelling power, solubility,
and digestibility
 The uniform particle size of the flour and the limited number of samples can increase the
homogeneity of heat transfer throughout the granule