title: Thermophilic enzymes and their impact on milk powder during storage

authors: Chen, Lin

abstract: Milk powder quality and storage life can be compromised by functionality and flavour defects. These defects can be the result of chemical or biochemical reactions, such as the Maillard (browning) reaction, proteolysis and lipolysis. The New Zealand dairy industry has set specifications for thermophile numbers in milk powders that have been used for many years as an indicator of microbial quality. However, any correlation between the numbers of these bacteria and product quality is anecdotal, and there is little supportive scientific evidence. 

This research has set out to: (1) survey the cause of the problem for off-flavours in milk powder storage, mainly whole milk powders (WMPs) because they are the largest powder-product, and most likely to have problems associated with flavour; (2) develop assay methods for detecting possibly very low levels of protease and lipase in the WMPs; and finally (3) determine enzymatic effects in the WMPs during storage. 

The study has focused on the detection of protease and lipase activities. Several sensitive and commonly used assay methods were applied in reconstituted milk made from different batches of commercial WMPs. Both protease and lipase activities were detected, and the lipase activity was quantified at 0.7-1.1 U/g powder (pNP caproate unit), but the level of protease activity is yet to be accurately determined. 

A lipase was semi-purified from a WMP using Phenyl Sepharose hydrophobic chromatography. The enzyme is most active at 60°C under the conditions used, and has similar substrate specificity to the lipases produced by seven Bacilli isolated from a milk powder production stream. Although the source of the powder lipase is yet to be identified, data suggest that it is most likely from a thermophilic bacterium. 

Preliminary studies on the characteristics of the proteases and the lipases produced by the seven Bacilli showed that the proteases differ between isolates in term of pH optima and heat-stabilities, so do the lipases. The lipases are more heat-stable than the proteases in a buffer system. Under the protection of milk proteins, these enzymes can survive the heat-treatments applied in the milk powder manufacture process, and retain activities in the powder. 

Further studies on WMPs spiked with thermophilic proteases and lipases, or taken directly from the commercial process have confirmed that the proteases and the lipases are active in the powder (at moisture < 5%) during storage. Proteolysis was observed as the increase of 1% trifluoroacetic acid (TFA) soluble protein fragments and the decrease of solubility, and lipolysis was shown as the release of free fatty acids (FFA). The lipases showed the same specificities in a buffer system and in the powder. The levels of enzymatic products increase with increasing storage temperatures and time. Proteolysis resulted in poor solubility of WMP within one week of storage at 37°C. Lipolysis resulted in the levels of FFA, especially short chain butyric and caproic acids, exceeding the organoleptic threshold values under the same storage conditions. 

Nevertheless, none of the defects observed showed any correlation with thermophile numbers - one of the current specifications for quality control of WMP. Therefore, it is not thermophiles per se that affect milk powder quality during storage, it is the heat-stable enzymes, from whatever source.

text: Thermophilic enzymes and their impact on milk powder during storage Milk powder quality and storage life can be compromised by functionality and flavour defects. These defects can be the result of chemical or biochemical reactions, such as the Maillard (browning) reaction, proteolysis and lipolysis. The New Zealand dairy industry has set specifications for thermophile numbers in milk powders that have been used for many years as an indicator of microbial quality. However, any correlation between the numbers of these bacteria and product quality is anecdotal, and there is little supportive scientific evidence. 

This research has set out to: (1) survey the cause of the problem for off-flavours in milk powder storage, mainly whole milk powders (WMPs) because they are the largest powder-product, and most likely to have problems associated with flavour; (2) develop assay methods for detecting possibly very low levels of protease and lipase in the WMPs; and finally (3) determine enzymatic effects in the WMPs during storage. 

The study has focused on the detection of protease and lipase activities. Several sensitive and commonly used assay methods were applied in reconstituted milk made from different batches of commercial WMPs. Both protease and lipase activities were detected, and the lipase activity was quantified at 0.7-1.1 U/g powder (pNP caproate unit), but the level of protease activity is yet to be accurately determined. 

A lipase was semi-purified from a WMP using Phenyl Sepharose hydrophobic chromatography. The enzyme is most active at 60°C under the conditions used, and has similar substrate specificity to the lipases produced by seven Bacilli isolated from a milk powder production stream. Although the source of the powder lipase is yet to be identified, data suggest that it is most likely from a thermophilic bacterium. 

Preliminary studies on the characteristics of the proteases and the lipases produced by the seven Bacilli showed that the proteases differ between isolates in term of pH optima and heat-stabilities, so do the lipases. The lipases are more heat-stable than the proteases in a buffer system. Under the protection of milk proteins, these enzymes can survive the heat-treatments applied in the milk powder manufacture process, and retain activities in the powder. 

Further studies on WMPs spiked with thermophilic proteases and lipases, or taken directly from the commercial process have confirmed that the proteases and the lipases are active in the powder (at moisture < 5%) during storage. Proteolysis was observed as the increase of 1% trifluoroacetic acid (TFA) soluble protein fragments and the decrease of solubility, and lipolysis was shown as the release of free fatty acids (FFA). The lipases showed the same specificities in a buffer system and in the powder. The levels of enzymatic products increase with increasing storage temperatures and time. Proteolysis resulted in poor solubility of WMP within one week of storage at 37°C. Lipolysis resulted in the levels of FFA, especially short chain butyric and caproic acids, exceeding the organoleptic threshold values under the same storage conditions. 

Nevertheless, none of the defects observed showed any correlation with thermophile numbers - one of the current specifications for quality control of WMP. Therefore, it is not thermophiles per se that affect milk powder quality during storage, it is the heat-stable enzymes, from whatever source.

year: 2000

title: Can nonhumans speak? Languaging and worlds in posthumanist applied linguistics

authors: Demuro, Eugenia

subjects: posthumanism

abstract: This paper mobilises posthumanism as a way to theorise and articulate what language(s)/languagingmay be for nonhuman animals. This is investigated via various concepts brought together: we turn to the on-tological turn in anthropology to expand on what language is, or might be, amongst humans, and then discussUmwelt and languaging as two possible modes of exploring ontologies and biosemiosis among nonhumans. Thedialogue between posthumanism and biosemiosis is so far absent in the field of critical language studies. Theaim, thus, is to contribute to the nascent field of posthumanist applied linguistics by tentatively linking discretefields of enquiry for a productive exchange across disciplines, and to further the discussion of how nonhumanlanguage is (or may be) ontologised

text: Can nonhumans speak? Languaging and worlds in posthumanist applied linguistics This paper mobilises posthumanism as a way to theorise and articulate what language(s)/languagingmay be for nonhuman animals. This is investigated via various concepts brought together: we turn to the on-tological turn in anthropology to expand on what language is, or might be, amongst humans, and then discussUmwelt and languaging as two possible modes of exploring ontologies and biosemiosis among nonhumans. Thedialogue between posthumanism and biosemiosis is so far absent in the field of critical language studies. Theaim, thus, is to contribute to the nascent field of posthumanist applied linguistics by tentatively linking discretefields of enquiry for a productive exchange across disciplines, and to further the discussion of how nonhumanlanguage is (or may be) ontologised

year: 2023-09-01

title: Ngā tohu o te taiao: Observing signs of the natural world to identify seastar over-abundance as a detriment to shellfish survival in Ōhiwa Harbour, Aotearoa New Zealand

authors: Paul-Burke, Kura

subjects: Tohu

abstract: Māori understandings and experiences of the natural world encompass not only what is known but how it is known, and the intergenerational connectedness of that knowledge with the environments from which it is derived. Ngā tohu o te taiao (hereafter ‘tohu’), or the cultural and environmental signs and indicators of the natural world, are widely used by kaitiaki or local practitioners to identify trends or changes in the state or health of marine taonga (culturally important) species and their associated environments (Paul-Burke, 2017). Māori worldviews position humans within nature and focus on ways in which cultural understandings and intergenerational connections between people and their bio-physical contexts assist in the retention and protection of biodiversity and ecologically sustainable ecosystems (Lyver et al., 2016). Tohu are a fundamental expression of kaitiakitanga or active guardianship and are based on the primal instinct of survival and recognising that in order to survive one must pay attention to the natural signs and signals thoughtfully, so as to manage our mahinga kai (food harvesting area) and ourselves into the future (Paul-Burke et al., 2020). This article considers the example of the over-abundant eleven-armed seastar (pātangaroa, Coscinasterias muricata; hereafter ‘seastar’) predating on culturally and ecologically important shellfish populations in a traditional mahinga kai of Ōhiwa Harbour in the Bay of Plenty region of Aotearoa/New Zealand. The over-abundance of seastars was considered a contemporary tohu of a degrading harbour. It was deemed imperative by iwi (tribe) members that a trial using quantitative methods to investigate predation pressure of seastars on the green-lipped mussel (kuku or kūtai, Perna canaliculus) population be conducted in the harbour. Between September 2018 and February 2019 field trials were undertaken that prioritised mātauranga Māori (Māori knowledge) alongside marine science to assist with a better understanding of the degrading harbour. It was hoped that the research would help and promote recovery, in particular but not limited to, the once abundant but now severely reduced mussel reefs in the soft-mud-bottomed harbour.

text: Ngā tohu o te taiao: Observing signs of the natural world to identify seastar over-abundance as a detriment to shellfish survival in Ōhiwa Harbour, Aotearoa New Zealand Māori understandings and experiences of the natural world encompass not only what is known but how it is known, and the intergenerational connectedness of that knowledge with the environments from which it is derived. Ngā tohu o te taiao (hereafter ‘tohu’), or the cultural and environmental signs and indicators of the natural world, are widely used by kaitiaki or local practitioners to identify trends or changes in the state or health of marine taonga (culturally important) species and their associated environments (Paul-Burke, 2017). Māori worldviews position humans within nature and focus on ways in which cultural understandings and intergenerational connections between people and their bio-physical contexts assist in the retention and protection of biodiversity and ecologically sustainable ecosystems (Lyver et al., 2016). Tohu are a fundamental expression of kaitiakitanga or active guardianship and are based on the primal instinct of survival and recognising that in order to survive one must pay attention to the natural signs and signals thoughtfully, so as to manage our mahinga kai (food harvesting area) and ourselves into the future (Paul-Burke et al., 2020). This article considers the example of the over-abundant eleven-armed seastar (pātangaroa, Coscinasterias muricata; hereafter ‘seastar’) predating on culturally and ecologically important shellfish populations in a traditional mahinga kai of Ōhiwa Harbour in the Bay of Plenty region of Aotearoa/New Zealand. The over-abundance of seastars was considered a contemporary tohu of a degrading harbour. It was deemed imperative by iwi (tribe) members that a trial using quantitative methods to investigate predation pressure of seastars on the green-lipped mussel (kuku or kūtai, Perna canaliculus) population be conducted in the harbour. Between September 2018 and February 2019 field trials were undertaken that prioritised mātauranga Māori (Māori knowledge) alongside marine science to assist with a better understanding of the degrading harbour. It was hoped that the research would help and promote recovery, in particular but not limited to, the once abundant but now severely reduced mussel reefs in the soft-mud-bottomed harbour.

year: 2022-03-28