Heriot-Watt University Research Gateway Mashing with unmalted sorghum using a novel low temperature enzyme system Citation for published version: Holmes, C, Casey, J & Cook, DJ 2017, 'Mashing with unmalted sorghum using a novel low temperature enzyme system: Impacts of sorghum grain composition and microstructure', Food Chemistry, vol. 221, pp. 324-334. https://doi.org/10.1016/j.foodchem.2016.10.083 Digital Object Identifier (DOI): 10.1016/j.foodchem.2016.10.083 Link: Link to publication record in Heriot-Watt Research Portal Document Version: Peer reviewed version Published In: Food Chemistry General rights Copyright for the publications made accessible via Heriot-Watt Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy Heriot-Watt University has made every reasonable effort to ensure that the content in Heriot-Watt Research Portal complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 19. Apr. 2022
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Heriot-Watt University Research Gateway
Mashing with unmalted sorghum using a novel low temperatureenzyme system
Citation for published version:Holmes, C, Casey, J & Cook, DJ 2017, 'Mashing with unmalted sorghum using a novel low temperatureenzyme system: Impacts of sorghum grain composition and microstructure', Food Chemistry, vol. 221, pp.324-334. https://doi.org/10.1016/j.foodchem.2016.10.083
Digital Object Identifier (DOI):10.1016/j.foodchem.2016.10.083
Link:Link to publication record in Heriot-Watt Research Portal
Document Version:Peer reviewed version
Published In:Food Chemistry
General rightsCopyright for the publications made accessible via Heriot-Watt Research Portal is retained by the author(s) and /or other copyright owners and it is a condition of accessing these publications that users recognise and abide bythe legal requirements associated with these rights.
Take down policyHeriot-Watt University has made every reasonable effort to ensure that the content in Heriot-Watt ResearchPortal complies with UK legislation. If you believe that the public display of this file breaches copyright pleasecontact [email protected] providing details, and we will remove access to the work immediately andinvestigate your claim.
Pickerell, & Axcell, 1993). The results illustrate that simply providing a greater593
content of fermentable sugar and FAN does not guarantee an efficient fermentation.594
The worts of the Mexican sorghum and agricultural white sorghum (Nigeria) from595
low-temperature mashing were of comparable fermentability and final alcohol yield to596
those produced using brewing cultivars. This was despite them having a lower starch597
content in the original grist (Table 1).598
The results obtained here suggest that worts produced using the low-temperature599
mashing system can result in fermentation alcohol yields comparable to the high-600
temperature mashing system. In addition, the low-temperature system appeared less601
dependant on the raw materials used. However, fermentation of the low-temperature602
mashed worts was relatively slow, indicating a deficiency in a component required for603
efficient fermentation or the presence of a component at inhibitory concentrations.604
4. Conclusions605
A novel low-temperature mashing system was shown to produce worts of comparable606
brewing value to those resulting from a more traditional, energy intensive, high-607
temperature mash. The energy savings of operating with the low temperature system608
would be substantial at industrial scale because i) Tmax for the schedule was reduced609
from 95°C to 78°C, ii) the energy requirements of heating a mash to 95°C and then610
cooling it back to 65°C to saccharify the mash are removed and iii) the overall mash611
schedule is shorter by approximately 2 hours. Furthermore, our results offer612
preliminary encouragement that the novel low-temperature mashing regime613
compensates for some raw material quality differences and narrowed the gap in614
brewing performance between the use of brewing and non-brewing sorghum cultivars.615
It thus has the potential to facilitate broader use of locally produced sorghum varieties616
in brewing, although full substantiation of this is beyond the scope of the present617
paper. The noted issue with long, sluggish fermentation times for the low temperature618
mashed worts is readily solvable in brewing practice. The excellent apparent619
fermentability results confirm that the worts had the required alcohol yield potential,620
albeit that the fermentations took a long time to attenuate. Fermentation vigour would621
most likely be improved by i) substituting different diastatic enzyme blends for the622
Amylo300 (amyloglucosidase) used here. This enzyme is not the component which623
confers the low temperature gelatinisation property and it generates high624
concentrations of glucose in worts which subsequently can slow yeast glucose uptake625
(Phaweni, O'Connor-Cox, Pickerell, & Axcell, 1993), or ii) the use of supplementary626
yeast nutrients (nitrogen source, Zn2+, etc.).627
With regard to the impacts of cultivar composition, starch properties and628
ultrastructure on brewing performance it was interesting to note that with either629
mashing schedule the impacts of kernel structure, and in particular evidence of strong630
starch-protein interactions had a far greater influence than did starch gelatinisation631
temperature – although the latter is more frequently used to assess likely brewing632
performance. Thus the noted lower gelatinisation temperature range for the red633
sorghum from Mexico did not offer a significant advantage in terms of extract or634
fermentable sugars yield. Whilst the brewing varieties were of lower protein content,635
protein per se did not correlate with mashing performance. Thus, the red sorghum636
contained the highest amount of protein (and tannins) but yielded respectable brewing637
performance, particularly when mashed using the low temperature regime. Hence our638
work suggests that it is the way in which protein is structured and in particular the639
strength of protein-starch granule interactions which most influenced brewing640
performance. Thus the white (Ghana) sorghum performed poorly using either mash641
schedule. The RVA profile represented the easiest way of identifying this sorghum as642
potentially problematic for brewing use.643
In the present work there was no support for the hypothesis that tannin levels644
negatively impact on brewing performance (with the levels of exogenous enzymes645
used here), although this was not the main focus of the study and no sensory tests646
were performed on beers to evaluate the levels of astringency conferred.647
648
Acknowledgements649
We gratefully acknowledge Diageo Global Beer Technical Centre and the British650
Biological Sciences Research Council (BBSRC) for their financial support of this651
work. The authors wish to thank Eoin Lalor and Kerry Ingredients and Flavours for652
supplying the mash enzymes used in the trials. With thanks to the Biomaterials group653
at Nottingham for use of their DSC and RVA facilities.654
Conflict of Interest655
The authors are not aware of any conflict of interest relating to publication of the656
enclosed material.657
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Table 1: Analytical data for the five sorghum cultivars used in the trial.
Results are the mean of triplicate independent mashes ± standard deviation. asum total of fructose, glucose, maltose and maltotriose.4
5
Figure 1: Details of A) traditional high temperature and B) novel low temperature mashing
regimes used in the research, together with details of the respective exogenous enzymes
added.
Enzymepreparation
Principal Activities Enzyme source Temperatureoptimum
pHoptimum
Amylo 300 amyloglucosidase A. niger 75 4.0Bioprotease P1 protease Bacillus spp. 70 6.0Hitempase STXL -amylase B. lichenformis 90 6.0MPA 5 -amylase A. oryzae 60 6.0
Promalt S-LTPAmylolytic andproteolytic
GM and non-GM strains
50-70 5.0-7.0
A)
B)
Figure 2 Scanning electron micrographs showing: Longitudinal cross section through an entire caryopsis ofA) yellow sorghum from Nigeria and B) white sorghum from Ghana. C) the border between floury andcorneous endosperm in the yellow (Nigeria) sample D) High magnification image of the floury endospermof yellow Nigerian sorghum E) corneous endosperm of the white Ghanaian sorghum and F) a starch granuleisolated from the white sorghum originating in Ghana, labelled with (i) protein body and (ii) indentation.
Corneous/floury
interface
Floury endosperm
Corneousendosperm
Flouryendosperm
Corneousendosperm
Corneousendosperm
Figure 3: RVA pasting profiles of (A) sorghum flours tested in water (B) sorghum flours tested in 10 mM silver nitrate and (C) extracted and
purified sorghum starches in 10 mM silver nitrate.
Results displayed are the mean of triplicate analyses.
40
50
60
70
80
90
100
0
500
1000
1500
2000
0 600 1200 1800
Tem
pe
ratu
re(°
C)
Time (s)
Yellow (Nigeria) Yellow (Cameroon) Red (Mexico) White (Nigeria) White (Ghana) temp