Life Cycle Assessment

Overview

Currently, aquatic products are vital component of sustainable food systems due to their unique high nutritional value, playing a significant role in global food security and poverty reduction efforts (1). However, the aquatic product industry still faces serious challenges, such as substantial spoilage losses and difficulties in managing solid waste. These issues not only cause significant economic losses but also impose environmental pressures and elevate public health risks, thereby hindering the development of the marine green economy (1). To address these issues, we developed a natural bio-preservative derived from crustacean waste. This aims to promote the recycling and utilization of crustacean waste, reduce spoilage-related losses of aquatic products during transportation and storage, and ultimately contribute to a circular blue economy that "sourced from aquatic products, used for aquatic products".

Life Cycle Assessment (LCA) serves as a crucial methodology for measuring energy consumption, analyzing cost trends, and evaluating safety risks throughout production and usage processes. As a comprehensive approach, LCA assesses the environmental impacts of a product across its entire life cycle-from raw material extraction and production to use and disposal-incorporating key factors such as energy consumption, greenhouse gas emissions, and cost accounting (2). Therefore, we conducted a Life Cycle Assessment to compareour natural bio-preservative, chitooligosaccharides (COS), with the chemical preservative potassium sorbate (PS). This allowed us to comprehensively evaluate the advantages of our product in terms of energy savings, cost reduction, and enhanced safety.

The functional unit for our life cycle assessment is 1 liter of preservative solution with equivalent antibacterial efficacy. The system boundary is defined as the "cradle-to-gate" process of product production, with the calculation boundary encompassing all inputs and outputs at the laboratory level during this stage, including chemical reagents/enzyme production, electricity consumption, etc. (2).

The equations for calculating environmental impact are as follows:

$$ C_T = C_P + C_F + C_D $$

$$ C_i = \sum_{j=1}^{n} a_{ij} I_{ij} $$

Where C_T is the total carbon emissions (kg CO₂eq), C_P is the carbon emissions from the product production process (kg CO₂eq), C_F is the carbon emissions during the preservation process (kg CO₂eq) and C_D is the carbon emissions from waste treatment (kg CO₂eq).

The carbon emissions for each step (C_i) are calculated using the input quantity (I_ij) and its corresponding carbon emission factor (α_ij).

The specific carbon emission coefficients are as follows:

Table 1 Carbon emission factors used in calculation.

The cost accounting calculation equations are as follows:

$$ P_T = P_P + P_F + P_D $$

$$ P_i = \sum_{j=1}^{n} a_{ij} U_{ij} $$

Where:

P_T is the total cost, P_P is the cost incurred during the product production process, P_F is the cost during the preservation process and P_D is the cost in the waste treatment process.

The cost for each step (P_i) is calculated based on the input quantity (U_ij) and its corresponding unit cost factor (α_ij). The specific unit cost factors are as follows:

Table 2 Unit cost factors used in calculating chemical-based production of potassium sorbate.

Environmental Impact

According to the colony count results from the preservation experiment (for details, refer to Results, POC), over the three days, the bacteriostatic rate of the enzymatically produced chitooligosaccharides preservative was 86.56%, while that of the 0.2% potassium sorbate solution was 57.55%. According to the logistic equation,

$$ y = \frac{A}{1 + e^{-k(x - x_0)}} $$

In the equation, y represents the bacteriostatic rate, x denotes the preservative concentration, A is the maximum upper limit of the bacteriostatic rate (typically close to 100%), x₀ is the half-maximal effective concentration (EC₅₀), i.e., the concentration required to achieve a 50% bacteriostatic rate, and k is the steepness of the curve, reflecting the sensitivity of microorganisms to the preservative (a higher k value indicates a steeper curve, meaning microorganisms are more sensitive to dosage changes).

The EC₅₀ of potassium sorbate in the microbial system is 100 mg/L, equivalent to 0.01% (8). Based on experimental bacteriostatic rates, it can be concluded that a potassium sorbate concentration of 1.17% exhibits efficacy equivalent to that of the enzymatically produced preservative.

Production of Enzymatic Chitooligosaccharides Preservative

In the production of enzymatic chitooligosaccharides preservative, the raw material used is chitosan derived from crustacean waste. Currently, crustacean waste is typically disposed of in landfills, which, according to data, generates 0.1 kg of CO₂ per kilogram of crustacean waste, posing significant environmental pressure (3).

In the enzymatic production of chitooligosaccharides, crustacean waste must first be converted into chitosan. Literature studies indicate that producing 1 kg of pure chitin requires 10 kg of dried snow crab shells, 1.2 kWh of electricity, 6 kg of coal for heating, 9 kg of 6% HCl solution, 8 kg of 4% NaOH solution, and 300 liters of freshwater. Additionally, steam emissions from industrial processes generate 0.9 kg of CO₂ per kilogram of polymer. Producing 1 kg of chitosan requires 1.4 kg of chitin, 5.18 kg of NaOH, 31 MJ (1.85 kg) of wood fuel, 250 liters of water, and 1.06 kWh of electricity (9, 10, 11).

Subsequently, we further process chitosan using enzymatic hydrolysis to produce the chitooligosaccharides preservative (see more in POC).

Finally, our calculations show that producing 1 liter of chitooligosaccharides preservative using this process route results in 0.0607 kg of CO₂ emissions. Thus, our production process holds significant importance in reducing environmental pressure and promoting a circular economy.

Production of chemical chitooligosaccharides preservative

In the chemical production of chitooligosaccharides, the method applied involved 0.5 wt% chitosan and 8 vol% H₂O₂, yielding chitooligosaccharides with a molecular weight of approximately 2000 Da and a production yield of 85% (12). According to the experimental results (see more in Result, POC), the antibacterial capacity of 20 mg/mL <2000 Da chitooligosaccharides is comparable to that of a 0.2% potassium sorbate solution. Assuming that the antibacterial capacity is directly proportional to the concentration, 116 mg/mL <2 kDa chitooligosaccharides would exhibit an antibacterial capacity equivalent to that of the preservative obtained by the enzymatic method. Based on the carbon emission factors of chitosan and hydrogen peroxide, it is estimated that the production of 1 L of 116 mg/mL <2 kDa chitooligosaccharides solution, which has equivalent functional efficacy to the chitooligosaccharides preservative, would result in emissions of 7.89 kg CO₂.

Chemical synthesis of potassium sorbate

In the synthesis of potassium sorbate, we selected the synthesis route using crotonaldehyde and ketene for the life cycle assessment of the product production phase. Based on calculations from the literature, the CO₂emissions from the production of each kilogram of potassium sorbate amount to 14.74 kg (13, 14). Consequently, the production of 1 liter of the functional unit of potassium sorbate solution would generate 0.172 kg of CO₂.

Summary

Using enzymatic hydrolysis of chitosan to produce chitooligosaccharides preservatives can greatly address the issue of crustacean waste disposal, thereby reducing greenhouse gas emissions and further mitigating the environmental crisis. This section demonstrates that, at the laboratory level, the enzymatic production of chitooligosaccharides emits only 0.0607 kg CO₂/L, significantly reducing emissions compared to the chemical method for producing chitooligosaccharides of equivalent efficacy. Compared to the chemical production of potassium sorbate with roughly equivalent efficacy, the enzymatic hydrolysis of chitosan reduces CO₂ emissions by approximately 30 times. This indicates that this approach is greener and more efficient than traditional processes, a ligning with the development direction of energy conservation and environmental protection.

Cost Analysis

TWe focused on the cost quantification of bacterial culture materials such as tryptone, yeast extract, NaCl, and the substrate chitosan. The production cost of chitosan was determined based on the production route outlined in Section 1.1. According to calculations, the production of 1 L of chitooligosaccharides preservative via the enzymatic method requires 0.43 RMB, while the chemical production of 116 mg/mL <2 kDa chitooligosaccharides with equivalent efficacy costs 11.91 RMB, and the chemical production of potassium sorbate with equivalent efficacy costs 1.52 RMB. Therefore, compared to the chemical production of chitooligosaccharides and potassium sorbate, the enzymatic production of chitooligosaccharides represents a more cost-effective technological route.

Safety Assessment

The inevitable release of raw materials during the production process not only harms the environment but also poses serious risks to the health of workers. Therefore, the transition toward greener and more efficient production processes has become an irreversible trend. Currently, exposure risks can be quantitatively evaluated using the Margin of Exposure (MOE) index (15).

$$ MOE = \frac{BMD}{Cexp} $$

$$ C_{\mathrm{exp},d} = \frac{A \left( \frac{g}{\mathrm{use}} \right) \times C_{\mathrm{ing}}(\%) \times D_{\mathrm{abs}}(\%) \times F\left( \frac{\mathrm{use}}{\mathrm{day}} \right) \times \left( \frac{1000\, \mathrm{mg}}{\mathrm{g}} \right)}{BW(\mathrm{kg})} $$

Here, BMD (Benchmark Dose) refers to the dose of a chemical substance that, when compared to the control group, can induce a specific adverse effect at a predetermined, slight but measurable level. C_exp represents the exposure concentration, A is the application amount, C_ing is the ingredient concentration, Dabs is the dermal absorption value, F is the frequency of substance application, and BW is the body weight.

The BMDL10 (Benchmark Dose Lower Confidence Limit) for crotonaldehyde is 0.30 mg/kg bw/day. A substance is considered high-risk when the MOE (Margin of Exposure) is less than 1. Calculations show that for an adult weighing 65 kg, working five days per week and producing 1 kg of potassium sorbate daily, the substance would not be classified as high-risk only if Dabs is less than 2.1*10^-7%. Therefore, the production process of potassium sorbate may involve significant safety risks. In comparison, enzymatic synthesis operates under milder conditions and utilizes reagents with lower toxicity, making it more beneficial for both environmental and personal safety.

Conclusion

The life cycle assessment conducted in this study compared the "cradle-to-gate" environmental impacts of enzymatically produced chitooligosaccharides preservative, chemically produced chitooligosaccharides preservative, and chemically synthesized potassium sorbate at laboratory scale. In the aspect of production of chitooligosaccharides, the enzymatic approach decreases about 99.1% of CO₂ emissions and 96.4% of cost compared to the chemical one. Additionally, our method saves about 61.0% of CO₂ emissions and 71.7% of cost compared to the chemical production of traditional preservative, potassium sorbate, in the same functional performance. The results demonstrate that the enzymatic production of chitooligosaccharides preservative represents a more promising, safer, and sustainable innovative technology. Thus, this approach can effectively reduce environmental burdens, contribute to the efficient development of a circular economy, and ultimately advance global public health initiatives.

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