What are auditors doing to protect against transmission or acquisition of SARS-CoV-2?
In the midst of the produce industry responses to the supply chain and marketplace disruptions from the SARS-CoV-2 (also called COVID 19 and coronavirus) pandemic, audits under the Global Food Safety Initiative (GFSI) benchmarked and FSMA-integrated audit schemes for Good Agricultural Practices, Good Handling Practices, Good Manufacturing Practice, and various other aspects of food safety systems are continuing. Audit service providers appear very uniform in providing assurance and sound policies for conducting ranch and facility site-audits and, as possible, virtual audits.

In line with the fluidity of guidance and specific protective measures from authoritative sources, these policies resonate with the current information provided by the WHO, CDC, FDA, CDC, and local, state and federal authorities in countries of their operation. Flexibility and accommodations for certificate extensions have been communicated to support the industry during this challenging time, if full audits must be delayed because of COVID-19.   A few examples are provided here for those interested in the measures being taken to protect the firm, its employees, and the auditors themselves as they must travel within and among affected regions. Some key elements include daily self-monitoring, 14-day self-isolation if having traveled from or through a restricted area, separate vehicle travel from firm’s host, frequent handwashing, and frequent sanitization of any hand-held equipment and clothing.  

Post-harvest water audit challenges have sparked controversy
Few produce safety control point operations have generated as much confusion and heated discourse as water quality management during postharvest cooling, washing, fluming, and quality retention treatments. This is triply true for recirculated water systems.

Prior to the coronavirus pandemic, the challenges of optimizing postharvest wash and cooling water quality management had once again risen to the forefront as the full FSMA ‘covered’ produce industry came into the compliance, inspection, and enforcement dates. Industry market-access, marketing association, and marketing order audit schemes reflected this increased expectation and scrutiny around scientifically valid water quality management parameters and verification programs. One of the more controversial compliance elements frequently arriving in my e-mail Inbox (nobody calls anymore) involves having a measurable and verifiable foundation for the frequency of partial or complete clean water exchanges. 

Added to this, several firms brought the issue of some auditors and inspectors insisting that measurement of turbidity (water clarity) in postharvest water uses is a compliance requirement, a must, of the FSMA Produce Safety Rule.  So, let’s deal with this here; I can find no evidence of this specific requirement or provision. Determining an effective and reproducible method for maintaining adequate water quality in postharvest applications is expected but not prescribed. 

One of the common battle lines has been drawn around the use of turbidity as the practical and inexpensive trigger for freshwater introduction to recirculated dump systems, flume transport, cooling, and wash/treatment water in postharvest handling. Freshwater replenishment is one key tool to maximize the performance and dose management of diverse antimicrobial treatments to postharvest water. This is essential to minimize the risk of cross-contamination within and among lots over time, whether hours or, in rare cases, days.  

Simply stated, turbidity is a simple and readily on-site deployable measurement but a limited indicator of an operational ability to manage microbial water quality in postharvest handling. Turbidity, or clarity, is an optical measurement of the light scattering properties of a liquid. For simplicity, let’s just say water. The intensity of light scattering is related to the specific traits and concentration of the materials in the water. These turbidity “factors” may include any single or combination of clay, silt, small and very small inorganic or organic suspended aggregates, dissolved organic substances, humic acids, and pigmented plant cell particulates and exudates to name a few.

The more suspended and dissolved materials in the water the greater the turbidity or cloudiness. Suspended particulates have been shown, in several recent studies and models of postharvest water quality, to provide a protective effect to human pathogens already attached to these surfaces or matrices. These particulates interfere with optimal dose efficacy of common water antimicrobials or prevent contact by their hydrophobic (water repelling) properties. 

Many operations have selected various methods to measure or judge postharvest water turbidity and use these adopted or in-house generated values to determine when to add fresh water or execute a full off-schedule water exchange, due to prevailing seasonal conditions. Obviously, dilution of particulates and reduction of dissolved organic compounds will benefit towards operating within scientifically valid limits and above any established critical food safety limits or levels provided as guidance. 

The controversy being encountered during inspections and audits arises when a turbidity standard has been set within a SOP and the firm is challenged to provide acceptable evidence of a reference validation study. These are exceptionally hard to come by. Very few peer reviewed studies accurately reflect the specific or even general commercial systems. Auditors or inspectors correctly observe that the boundaries of experimentally defined limits may be difficult to manage with accuracy (correct) and precision (consistent) in commercial systems. Those studies which do, based on on-site testing, typically report a low correlation to predicting antimicrobial dose-management control and achieving microbial water quality management goals, based on turbidity measurement alone. 

Interestingly, all sources of turbidity are not the same. It would be very easy to get deep into the weeds on this subject. You might even be ready to take a weedwhacker to this, but it is complex and specific to the situation and there are a number of recent journal papers and a few lengthy reviews on the topic. Suffice it to say that all current research points to the fact that all turbidity is not created equal.

The same measured turbidity in different soil and organic constituent burdens may be perfectly adequate or inadequate to facilitate antimicrobial dose uniformity and maintenance. These differences directly influence the risk of cross-contamination of foodborne pathogens (primarily bacteria) in recirculated postharvest water. In some water systems a turbidity of 300-500 NTU (the units of clarity; FAU is an alternative unit but comparable) comprised of dissolved simple organic compounds would be excessive to prevent microbiological exceedances. In recirculated water with largely inorganic soil, with low humic acids and other sources of phenolic compounds, 1500 NTU may be a manageable operational upper limit.     

This same body of research, from several research groups, points to Chemical Oxygen Demand (COD) as one of the better correlating traits to predicting the typical and worst-case accumulation of acute and long-term chlorine demand as raw or minimally-processed product and non-product materials (such as soil, leaf debris, decayed or damaged product) is added repeatedly to water systems. Even here, the specific composition that makes up the COD matters. Much of the focus has been on hypochlorite’s (chlorine) as the more impacted antimicrobial as compared to peroxyacetic acid and other effective organic acids, such as lactic acid. However, specific components of a system’s turbidity will interfere with these formulation’s efficacy and, as with chlorine and chlorine dioxide, can interfere with accurate dose measurement. 

The current research is detailed, systematic, and robust but still very difficult to derive and develop simple guidance for end-users. One good source for open access to these details is available at, a website dedicated to the outcomes of a large multi-investigator and multi-institution project under the Principal Investigator leadership and administrative coordination of Dr. Yaguang (Sunny) Luo (  

There are many in-line turbidity sensors and combined turbidity and conductivity sensors for commercial systems. My lab at University of California-Davis had an opportunity to conduct multi-visits to a grower-shipper to assist with assessing a newly installed hydrocooler management system with an in-line turbidity sensor, in-line PAA sensor, and suspended solids removal system. Focusing just on turbidity, the in-line sensor gave a different but very consistent read-out compared to a replicated ‘grab-sample’ from the system return water. Compared to the portable colorimeter, the sensor reading was always lower but uniformly so over several visits. With this outcome, it would be possible to derive a correction factor and use the on-site verification values, together with the other measurements of COD, dose, and microbial water quality control, to establish process control parameters.   

Lastly, there is a growing interest in the potential for using ultraviolet light absorbance at 254 nm (UV254) as a surrogate for COD measurements. Several labs have been evaluating the predictive value as a real-time measure of antimicrobial demand. Thus far, across several fresh and fresh-cut commodities, the results have shown good but, again, incomplete correlations and a limited consistency across reported studies. However, as in many imperfect systems, integrating multiple measurements in models being developed would appear to provide a functional and practical approach to improved postharvest wash water management for food safety and quality.     

About the information: This outreach article was developed as part of the objectives of National Institute of Food and Agriculture, U.S. Department of Agriculture, agreement number 2016-51181-25403.

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