Abstract

Proteins are one of the
four macromolecules in food and are the building blocks in-order for life to be
sustained. They catalyse reactions in all forms of life including
microorganisms, plants, and animals. Another function of proteins is to provide
structural support to tissues.

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In relation to industrial
proteins, they are present in every food industry from Dairy to Seafood to
Meat. The protein industry is a highly lucrative sector that contains high
profit margins.

A waste
stream is the flow of waste from domestic or industrial areas through to final
disposal.

Considering the vast
amount of waste being produced by food companies, it is imperative that
suitable methods of recovery of valuable products such as protein, are
established.

The current review
provides an in depth critical review of processes that are involved in protein
recovery and highlighting the recent advances made in the recovery industry,
according to research and literature present on the subject.

Methods of recovery
depend on different waste streams. The main technology used for the recovery of
protein is membrane technology. In whey protein recovery the main method used
is membrane filtration separation, it is known as one of the most viable
methods of protein recovery.

Membrane filtration
includes processes such as pre-treatment, ultrafiltration. microfiltration,
nanofiltration, osmosis and reverse osmosis.

Other methods of membrane
technology include precipitation separation, anion exchange membranes and
membrane distillation.

More recent methods of
protein recovery from waste streams include Liquid Chromatography, Foaming
process, Ultraviolet irradiation and gradient temperature assisted autolysis,
Chitosan and FeCL3

This review also looks at
the real benefits for companies and the environment by recovering protein from
waste streams and the cost involved in doing so, this paper will investigate
the true meaning of what is meant by from “gutter to gold”. (Geoffrey W. Smithers.,2008)

 

Introduction

Whey is the main
by-product of the dairy industry which is mainly produced during the production
of cheese and casein. Due to whey having a large organic content it also has a
very high BOD (Biochemical Oxygen Demand). Whey is known to be one of the
strongest industrial waste stream pollutant of any kind (E. Fuda et al. 2004)

According to (Bipasha Das
et al, 2015) it exhibits a BOD ranging from 30
to 50gL-1.

An example of an
environmental concern is seen with regards to the world meat industry. The
industry generates a pollutant load of 1.7×106 ton yearly of BOD due
to waste blood only, this is equivalent to the organic waste pollution caused
by 11 million people (Dart 1974)

Aside from whey proteins,
all waste streams or processing effluent are very rich in BOD, the presence of
proteins and amino acids cause these high levels. High BOD negatively effects
the environment.

Considering the vast
amount of whey being produced on a global scale (about 145 million tons per
year) (Sparsh Ganju et al, 2017), it is very important to develop new
approaches in properly dealing with the effluent instead of allowing it to
become waste and cause environmental damage.

Waste treatment has not
just been a challenge for the dairy and meat industry but also for the potato
and seafood industries respectively. With a reported figure of 300,000 ton of
shrimp head waste in China annually (Wenhong Cao et al, 2014), failure to properly dispose or recover nutrients from
the waste leads to extreme environmental implications.

Potato processing waste
is also an environmental concern due to the high concentrations of potassium
and Chemical Oxygen Demand (COD). These high concentrations are cause by the
presence of starch, proteins, amino acids and sugars. This results in expensive
waste treatment processes to the companies with no economic benefit

Due to the sheer problem
caused by effluents on the environment people began thinking what else could
they do with these waste streams. Over the last few decades it has been
recognised that these waste streams can have nutritional and functional values.
It was concluded that waste streams in all mentioned food industries contained
high amounts of valuable by-products which includes protein which then led on
to ideas of recovering this protein from the waste effluents.

Companies began to realise
the economic benefit of the utilization of protein from waste streams

Companies began to
investigate the benefits and the cost implications of protein recovery. Dairy
companies discovered the high profit margins available to them with the utilization
of whey protein, potato companies realised the high functionality and
nutritional value of the protein, Patatin, found in potato waste streams
(Friedman:1996). The meat industry discovered the benefits of
recovering protein from slaughterhouse waste and meat processing plant waste
and finally the seafood industry realised the recovered protein from fish waste
could be incorporated back into fish based foods, aquaculture feeds and a media
for microorganisms to grow. (Cavalheiro souza & Bora 2007 Rustad, Storro & Slizyte, 2011).

 

 

 

 

 

 

 

 

 

 

 

How is protein recovered from waste streams?

Many of the already
mentioned food sectors have decided to put special emphasis on the recovery of
nutrients from waste streams, protein in this case. This review provides an in
depth understanding of the different methods and applications for the recovery
of protein from waste.

(A)Membrane
technology has been successfully employed for
protein recovery from waste streams in the dairy industry for years.

What is membrane technology?

According to (Winston Ho
and Sirkar 1992). It is a separation technology that uses semi permeable
membrane filters to concentrate or fractionate a feed stream of liquid (i.e.
waste stream), resulting in two product streams. The compounds which pass
through the semi permeable membrane with the liquid, is known as the
“permeates” and the liquid retained is known as the “retenate” also known as
the rejected liquid (S. Ganju et al, 2017)

Membrane separation
methods are identified as the most viable methods for protein recovery at this
moment in time (Sparsh Ganju et al, 2017 )

The most widely used
processes to separate components such as whey protein and casein in the dairy
industry are Microfiltration, Ultra-filtration, and Reverse osmosis.

Ultrafiltration is a
process where proteins can be efficiently recovered resulting in a high yield
and purity. (Atra et al, 2005)

Before Ultra-filtration,
Pre-treatment must take place this involves the removing of suspended fat and
casein particles by microfiltration. It also helps to reduce the fouling of the
ultrafiltration membrane. (Cancino et al.,2006)

Different Membranes have
different percentage recovery of proteins in a study (by Charis M. Galanakis et
al, 2014) investigating protein recovery from
cheese whey on a Cypriot cheese known as Halloumi it was found that the optimum
separation of proteins with non-reducing sugars was using 20kDa-polysulphone
(GR70PP) and 2kDa Polyethersulphone (GR96PP) membranes. The percentage protein
recovered was between 87-90% which is extremely high.

According to (Sparsh
Ganju et al., 2017). “Membrane
fouling is caused due to a combination of different phenomena such as
concentration polarisation and pore blocking or cake formation”. The transfer
of mass through a membrane becomes limited due to the formation of deposits on
the membrane during the separation of proteins.

 Two main proteins that get stuck in the
membrane pores are alpha lactoglobulin and beta lactoalbumin. The caking of
these proteins to the membrane surface reduces the efficiency of the separation
technology. (Sparsh Ganju et al., 2017) 

As membrane fouling is a
major issue, pre-treatment must be carried out to limit it from taking place.

In whey ultrafiltration
production there are two main problems faced by companies. These are whey
protein recovery and membrane fouling. In a study conducted by (Wang Wen-Qiong
et al 2016),
they investigated the cross linking of the protein transglutaminase (TG)
catalysis as a membrane coupling protein. The study found the optimal
conditions for protein recovery included the Catalyzation of whey protein cross linking with TG
(40U/g whey proteins) at 40? for 1 hour at a PH value of 5. It was concluded
under these conditions the recovery rate was increased by 15-20%.

Whey protein:

Fig 1 Distribution of global whey production and
consumption (Tsakali et al.2010) (S. Ganju., 2017)

 

Whey protein separation
consists of three stages; Pre-treatment, separation, and drying (S. Ganju et
al., 2017)

 

 

Pre-treatment:

Microfiltration
predominantly used as a pre-treatment to avoid problems in the separation and
drying process.                                      

Separation:

Membrane technology is
the most common method of recovery of protein, with ultrafiltration being the
highest contributor in the recovery. There are lots of other separation methods
these will also be highlighted later in the paper.

Drying:

For commercial use whey
protein needs to be in a powder form i.e. (dried) in order to reduce its
transportation cost, accessibility for the consumer and to prolong its shelf
life. Drying results in a decrease of the alpha helix and random structure and
therefore increasing beta sheet structure in recovered proteins. (Bispasha Das
et al., 2015).

The two main methods of
drying are Spray drying and Freeze drying. The major challenge of spray drying
is that with such a high temperature present in the spray dryer, can cause
protein denaturation. Freeze drying has the advantage of a vacuum operating at
lower temperature thus not posing the threat of
denaturation of the protein.

Fig1.
Flow chart representing the recovery of whey protein (Bispasha Das et al.2016)

Although membrane
filtration is the most widely used protein separation technique, there are many
more that have been developed in recent years. These include;

Membrane
distillation- Unlike membrane filtration membrane distillation is
thermally driven. The heat for the process comes from solar heat. It uses a
hydrophobic membrane ensuring that only water vapour is allowed pass.
Separation is due to the phase change. With the
hydrophobic membrane displaying a
barrier for the liquid phase this results in allowing the vapour phase
(e.g. water vapour) to pass through the pores of the membrane.(Abdullah Alkhudhiri et al, 2012). The method is said to be quite promising according to recent research but requires further
study into the scale up aspects (S. Ganju et al., 2017).

Anion
exchange membranes – These are separations that are
based on ion exchange, they are driven by electrostatic interactions between
the charges on the surface of biomolecules such as proteins and clusters of
charged groups on membranes (S.
Ganju et al., 2017) the choice of anion exchange should be such that protein
denaturation will not occur. A buffer salt is released when the adsorbing of
the biomolecule displaces ions which are associated with the surface known as
counter ions. In this case the elution of the adsorbed proteins was carried out
by the salt solution NaCl. (S. Ganju et al., 2017).

Precipitation -This
recovery technique is achieved by the introduction of heat or the addition of
certain chemicals that cause the protein to precipitate. When heat is
introduced the formation of aggregation takes place these settle out of the
solution and therefore can be easily removed. A problem area in this technique
is the possibility of the denaturation of the proteins. The process of
selective precipitation is based on the use of solvents such as acetone.     

Other methods

(B)Liquid
chromatography

Liquid chromatography is
one of the most popular occurring method for the recovery and purification of
proteins (A.M.Ventura et al.,2008). According to (Maria
Joao Santos et al 2011) this technique is based on hydrophobic interaction
between hydrophobic ligands and non-polar regions on the surface of the
biomolecule (protein) (R.C.F.Bonomo et al 2006).HIC can be used as a first step
of an integrated process for the full recovery of proteins (i.e. whey) (Maria
Joao Santos et al 2011)

(C)Foaming
Process

Mainly used for mussel
blanching waste, Foam separation can be used for the recovery and enrichment of
proteins from processing wastewater obtained from the industrial blanching of
green lipped muscles (N.Y.Chan et al, 2006)

Foaming removes surface
active organic substances such as protein from waste liquid streams (J.D. Van
Der Toorn,1987). Protein which is known as a surface- active substance attaches
to the foam, so the foam is concentrated with proteins and the liquid remaining
is clarified (J.D. Van Der Toorn,1987)

PH is an important factor
to control in the foaming process as it effects the recovery of the protein due
to the changes of the isoelectric point of the protein molecule. (D.J. Shaw et
al, 1989), (G.T. Jeong et al, 2004), (Z. Zhang et al, 2004)

The conclusion of this
study by (N.Y.Chan et al.,2006) stated that “foaming experiments showed that
the protein enrichment ratio was inversely proportional to the volume of foam
generated and the protein recovery percentage”. Protein recovery ranged from
50-85%. Ph 5.2 was the optimum PH value according to the study and a air flow
rate of 2.2 L/min.

Table 1. Results from air flow rate experiments
(N.Y.Chan et al.,2006)

Air flow rate (L/min)

Foam volume (mL)

Enrichment ratio

Recovery percentage

1.0

830

1.48

15.9

1.4

330

2.27

9.7

1.8

930

1.95

23.4

2.2

5410

1.16

80.9

 

(D)Ultraviolet
irradiation and gradient temperature assisted autolysis

The head of a white
shrimp can degrade tissue proteins through a process called autolysis. (Cao,
Zhang, Hong & Ji 2008). The study led by Wenhong Cao investigated the
hypothesis of Ultraviolet irradiation and gradient temperature assisted autolysis
abilities in recovering protein from shrimp waste. This process is known as an
efficient and a relatively cheap process for the recovering of protein from
shrimp head waste streams. Enzymatic Hydrolysis methods have been widely
researched and investigated as a method for recovering protein from shrimp
waste. (Wenhong Cao et al., 2014). The conclusion of the investigation by
(Wenhong Cao et al., 2014) was that UV radiation can activate what is known as
the endogenous enzymes in shrimp head waste resulting in and increased percentage
of protein recovered.

(E)Chitosan
and FeCL3

Studies were carried out
for the optimization of conditions for protein recovery. A study spearheaded by
Xiaolin Chen (2006) investigating the recovery of protein from wastewater
during production of chitin (Xiaolin Chen et al 2006).
The results of the study showed that a PH value of 6.00 for wastewater, a
dosage of 1% chitosan solution in 1% acetic acid solution of 2.0ml for 50ml
wastewater and 1%FeCL3 aqueous solution of 2ml for 50 ml wastewater,
the flocculation time of 4.0h were the optimal conditions for the recovery of
protein. (Xiaolin Chen et al 2006).

In this study chitosan
was used as agulant and FeCl3 was the coagulant aid to recover
protein from discharged water.

 

Table
3. The recovery rate of protein when added different dosage of CTS, FeCl3 and
flocculated for different time

Dosage or time (ml or h)

The recovery rate of protein (%)

1

2

3

0

70.36 ± 0.02

81.8 ± 0.03

0.5

86.08 ± 0.02

74.71 ± 0.04

1.0

88.33 ± 0.04

76.47 ± 0.02

1.5

84.52 ± 0.03

2.0

78.57 ± 0.01

84.52 ± 0.01

71.76 ± 0.02

2.5

83.33 ± 0.03

3.0

78.2 ± 0.03

4.0

82.14 ± 0.04

75.28 ± 0.01

5.0

72.36 ± 0.03

6.0

77.38 ± 0.02

8.0

80.52 ± 0.03

10.0

80.48 ± 0.01

 

1, 2 and 3 showed the effect of the dosage of CTS,
FeCl3 and flocculation time on the recovery rate of protein,
respectively. (Xiaolin Chen et
al 2006).

 

 

 

 

Benefits of recovering protein and the commercial uses
of the recovered protein.

Whey Protein

Whey protein is the one
of the best known recovered protein from waste streams. It is also one of the
most lucrative industries in the world.

Fig. 4. Schematic
representation of the relative increase in value of whey protein/peptide
products with increasing underpinning scientific knowledge of whey solids, and
advances in technology and marketplace sophistication over the past
approximately 50 years. The dollar values indicated for products and the
chronology are not intended to be prescriptive, rather to provide a guide to
the types of products developed, their relative value, and approximate
developmental timeframes for the period indicated(Geoffrey W. Smithers., 2008)

The main result of whey recovery from cheese curd is
whey protein concentrate a substance that is used as a sports nutrition
supplement and is known to build muscle.

It is also reported that whey protein powder not only
help to promote weight loss but also lowers cholesterol and blood pressure if
used as a dietary supplement.

Whey protein is used as an alternative to milk
for people with lactose
intolerance, for replacing or
supplementing milk-based infant formulas, and increasing glutathione (GSH)
in people with HIV disease (Ranjan Sharma, 2010)

The recovered whey concentrate can also be used as
ingredients in yogurt, dairy desserts, and meat products. (Charis M.
Galanakis,2014 et. al)

With increasing restrictions and concerns
environmentally as well as the discovery of the nutritional and functional
properties of whey it began to be recognized as valuable resource in its
potential use in functional food, nutraceuticals, pharmaceuticals, and
cosmetics, (A Saxena, et al, 2009)

Animal Waste

In relation to the recovery of protein from animal
waste (i.e. slaughterhouse waste) there are also a vast range of uses for this
protein. It is transferred into a powder concentrate suitable for human
consumption but more interestingly, increasingly used for animal feed to
improve protein content of the feed. This shows that a cycle is visible with
the reuse of waste material back into food use for the animals.

Potato Protein

Potato protein recovered from waste potato processing
streams have high functionality and nutritional value and can be utilized in
food applications if recovered in native form and if isolated by methods that
prevent denaturation. (Ghosh, 2003). Protein recovered from potato processing
streams is used commercially usually as a protein additive. A protein additive
increases protein in a food not rich in protein.

Cost

As there is so many benefits of recovering protein for
example economic and environmental benefits. There is a cost in recovering
protein economically. For company to produce a food it`s an expensive process
and the utilization of the waste from this process is even more expensive.

Where cost is most visible is in whey production
recovery facilities where the use of these concentrates is commercially sought
after. For example, according to food company Glanbia PLC they invested a
further 21 million euro in 2012 on their whey protein facilities. They also
must factor in additional costs i.e. sundry expenses, wages etc.

According to the Industrial
Environmental Research Lab US, protein recovery from blood involves a large
cost to set up a recovery unit with low running costs the return tends to
exceed the investment after time.

In sum, benefits economically and environmentally outweigh the cost
aspect, return from protein recovery is a near assurance for 95% of companies.
If recovered protein is not for the commercial area it can be used in-company
therefore reducing output costs and increasing yield of a certain food product.

 

Conclusion

Protein recovery from
waste streams is getting increasingly important as time goes on.  As the world population increases, the demand
for food is greater. Larger food production results in higher volumes of waste
produced. Harvesting all that is good in waste streams was never more
important. This is beneficial to not only food companies in terms of higher
profit margin but it is also critical in feeding a growing world population and
the protection of the environment.

There has been a lot of
research and investigation into protein recovery from waste streams but more is
needed, new methods need to be investigated and introduced that delivers on all
levels.

The advances made in
protein recovery have been incredible, but they are not without their flaws.
With problems of heat denaturation, fouling of membranes and strength of
chemicals used are all problems that need to be addressed in the near future.

There are new methods of
protein recovery being tested, investigated, and researched in recent years for
example solvent precipitation, chromatography, and foaming process but these
are still not ready for large scale development.

The benefits of a good
protein recovery system are huge not only are companies keeping in line with
BOD, COD, and discharge legislation. The economic return for final products of
protein recovery is immense.

There really is a true
meaning behind the phrase from “gutter to gold”

 

 

 

 

 

 

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