<PAGE>   1
                                                                   EXHIBIT 10.48


FIFTH AMENDMENT AGREEMENT (THE "FIFTH AMENDMENT") TO THE REVOLVING LOAN
AGREEMENT WITH SECURITY INTEREST ENTERED INTO BY AND AMONG GRUPO INDUSTRIAL
SANTA ENGRACIA, S.A. DE C.V. (`BORROWER"), AS BORROWER, INDUSTRIAS CITRICOLAS DE
MONTEMORELOS, S.A. DE C.V. ("ICMOSA") AND AGROMARK, S.A. DE C.V. ("AGROMARK"),
AS GUARANTORS, THE UNIMARK GROUP, INC. ("GROUP"), AS GUARANTOR AND PLEDGOR, MR.
RAFAEL VAQUERO BAZAN AND MR. JOSE MARIA MARTINEZ BORHEZ, AS PLEDGORS, AND
COOPERATIEVE CENTRALE-RAIFFEISSEN BOERENLEENBANK B.A. "RABOBANK INTERNATIONAL"
("BANK"), AS LENDER.

                                    RECITALS

         A. Borrower and Bank executed a Revolving Loan Agreement with Security
Interest on April 10, 1997 by means of which Bank, subject to the terms and
conditions set forth therein, extended to Borrower an uncommitted U.S.
$8,500,000 (Eight Million Five Hundred Thousand Dollars, currency of the United
States of America) revolving loan facility, as amended by the Amendment
Agreement dated April 30, 1998 (the "FIRST AMENDMENT"), the Second Amendment
Agreement dated December 31, 1998 (the "SECOND AMENDMENT"), the Third Amendment
Agreement dated June 9, 1999 (the "THIRD AMENDMENT"), and the Fourth Amendment
Agreement dated June 1, 2000 (the "FOURTH AMENDMENT") (collectively, the "LOAN
AGREEMENT").

         B. ICMOSA and Agromark executed the Loan Agreement in order to
guarantee the punctual payment of the Gise Obligations (as defined in the Loan
Agreement") by Borrower (the "AFFILIATE GUARANTY").

         C. On April 10, 1997, Group executed a Guaranty in favor of Bank, as
such document has been ratified and amended by certain amendments dated as of
April 30, 1998 and December 31, 1998 (collectively, the "GROUP GUARANTY"), by
means of which Group guaranteed the punctual payment of the Gise Obligations by
Borrower.

         D. On April 10, 1997, Group, Pledgors and Bank executed a pledge
agreement, as amended by that certain amendment agreement executed by those
parties on May 29, 1997, ratified by that certain agreement dated as of April
30, 1998, by means of which Pledgors pledged in favor of Bank 100% of the issued
and outstanding stock of Borrower, ICMOSA and Agromark in order to guarantee the
punctual payment of the Gise Obligations by Borrower, with the amount of stock
of GISE being pledged being reduced to 48% of the issued and outstanding stock
of GISE pursuant to that certain second amendment agreement dated as of February
21, 2000 (collectively, the "PLEDGE AGREEMENT"). Borrower, Guarantors, Group,
and Pledgors are referred to individually as a "LOAN PARTY" and collectively as
the "LOAN PARTIES."

         E. The Loan Agreement was recorded before the Public Registry of
Commerce of the city of Cuidad Victoria, State of Tamaulipas under number 46,
volume 96, book 2.

         F. Borrower and its Affiliates and Bank executed a Waiver of Defaults
dated as of August 12, 1998, by the terms of which Bank waived certain defaults
existing under the Loan Agreement.

         G. Borrower and its Affiliates and Bank executed a Waiver of Defaults
dated as of April 14, 1999, by the terms of which Bank waived certain defaults
existing under the Loan Agreement.

         H. By letter dated July 19, 1999 (the "JULY 1999 LETTER"), Bank advised
Borrower that (1) Bank was exercising its right, pursuant to Section 2.13 of the
Loan Agreement, to deny Borrower's request for further advances under the Loan
Agreement, (2) any outstanding requests not yet funded would not be funded, and
(3) all outstanding advances were to be repaid as they matured in accordance
with the Loan Agreement.

         I. By letter dated August 11, 1999, (the "AUGUST 1999 LETTER") Bank
advised Borrower that notwithstanding the July 1999 Letter, that as each
outstanding Advance under the Loan Agreement came due, such Advance could be
renewed for successive thirty (30) day periods.



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         J. Borrower and Bank executed a Waiver of Defaults dated as of November
12, 1999, by the terms of which Bank waived certain defaults existing under the
Loan Agreement and reduced the Commitment under the Loan Agreement to $4,250,000
(currency of the United States of America).

         K. Borrower and its Affiliates and Bank executed a Waiver of Defaults
dated as of April 12, 2000, by the terms of which Bank waived certain defaults
existing under the Loan Agreement.

         L. Group executed a Collateral Assignment of Note and Security dated as
of June 1, 2000 (the "COLLATERAL ASSIGNMENT") for the benefit of Bank pursuant
to which Group collaterally assigned to Bank as additional security for the Gise
Obligations that certain Four Year Secured Term Note dated October 2, 1999,
executed by SFFI Company, Inc., payable to the order of Group in the original
principal amount of $1,100,000.00, with interest as therein provided (the
"COLLATERAL NOTE") and all security for the Collateral Note.

         M. UniMark Foods, Inc. ("FOODS"), as borrower, and Bank are parties to
a Revolving Credit Agreement dated as of February 12, 1997, as amended by that
First Amendment to Revolving Credit Agreement dated October 7, 1997, the Second
Amendment to Revolving Credit Agreement dated November 14, 1997, the Third
Amendment to Revolving Credit Agreement dated of May 22, 1998, the Fourth
Amendment to Revolving Credit Agreement dated as of December 31, 1998, the Fifth
Amendment to Revolving Credit Agreement dated as of May 17, 1999, the Sixth
Amendment to Revolving Credit Agreement dated as of January 3, 2000, the Seventh
Amendment to Revolving Credit Agreement dated as of March 1, 2000, the Eighth
Amendment to Revolving Credit Agreement dated as of March 31, 2000, and the
Ninth Amendment to Revolving Credit Agreement dated as of June 1, 2000
(collectively, the "U.S. CREDIT AGREEMENT"), and such revolving loan in the
original principal amount of $8,000,000 now outstanding to Borrower from Secured
Party under such Credit Agreement matures on January 1, 2001, and is evidenced
by the Sixth Renewal Revolving Note dated as of June 1, 2000 (the "U.S. NOTE").

         N. The obligations of Foods to Bank under the U.S. Credit Agreement are
secured by, among other things: (i) Security Agreements dated February 12, 1997
by and between Bank and each of Foods, Group, UniMark International, Inc. (a
wholly-owned subsidiary of Group, "INTERNATIONAL"), and Simply Fresh Fruit, Inc.
(a wholly-owned subsidiary of Foods, "SFFI") (the "U.S. SECURITY AGREEMENTS");
(ii) Pledge Agreements dated February 12, 1997 by and between Bank and each of
Foods and Group (the "U.S. PLEDGE AGREEMENTS"); and (iii) Unconditional Guaranty
Agreements dated as of February 12, 1997 by and between Bank and each of
International and SFFI (collectively, the "U.S. GUARANTY").

         O. ICMOSA, as borrower, and Bank executed a Revolving Loan Agreement
with Security Interest on April 10, 1997 (the "ICMOSA LOAN AGREEMENT") by means
of which Bank, subject to the terms and conditions set forth therein, extended
to the ICMOSA an uncommitted U.S.$7,500,000 (Seven Million Five Hundred Thousand
Dollars, currency of the United States of America) revolving loan facility,
which ICMOSA Loan Agreement was thereafter amended.

         P. The Group Guaranty guaranties the obligations arising under the
ICMOSA Loan Agreement as well as the Gise Obligations, and the Pledge Agreement
secures the obligations arising under the ICMOSA Loan Agreement as well as the
Gise Obligations. The Collateral Assignment secures the obligations arising
under the U.S. Credit Agreement and the ICMOSA Loan Agreement as well as the
Gise Obligations.

         Q. Effective as of the date hereof, all of the obligations arising
under the U.S. Credit Agreement and all of the obligations arising under the
ICMOSA Loan Agreement are being paid in full, and the U.S. Credit Agreement and
the ICMOSA Loan Agreement are being terminated.

         R. The Loan Parties wish to ratify the continued validity of the
Affiliate Guaranties, the Group Guaranty, the Pledge Agreement, and the
Collateral Assignment. Further, Borrower and Bank have agreed to amend certain
provisions set forth in the Loan Agreement.

         NOW, THEREFORE, in consideration of the foregoing and for other good
and valuable consideration, the receipt, sufficiency and adequacy of which are
hereby acknowledged, the parties hereto agree as follows:




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         1. LOAN DOCUMENTS ARE IN FULL FORCE. Except as specifically provided
herein, all the terms of the Loan Agreement, the Promissory Notes, the Group
Guaranty, the Pledge Agreement, the Collateral Assignment, and the other Gise
Loan Documents (as defined in the Loan Agreement) and their related documents
are unaffected hereby and remain in full force and effect.

         2. SAME TERMS. All terms used herein which are defined in the Loan
Agreement shall have the same meanings when used herein, unless the context
hereof otherwise requires or provides. In addition, all references in the Loan
Agreement and in the Gise Loan Documents to the "Agreement" shall mean the Loan
Agreement as amended by the First Amendment, the Second Amendment, the Third
Amendment, the Fourth Amendment, and this Fifth Amendment and as the same shall
hereafter be amended from time to time.

         3. AMENDMENTS TO LOAN AGREEMENT. Effective as of September 1, 2000, the
following changes shall be made to the Loan Agreement:

            a.    Section 5.17(b) of the Loan Agreement, "Current Ratio," is
                  deleted in its entirety.

            b.    A new paragraph (c) to Section 2.04 is hereby added, which
                  shall read as follows:

                  "In consideration for Bank's agreement to make certain
            reductions in the interest rate being charged on Advances made
            between the date hereof and January 1, 2001, Borrower agrees that in
            the event that Borrower fails to pay the Gise Obligations in full on
            January 1, 2001, Borrower will pay to Bank deferred interest in an
            amount equal to U.S.$85,000 (eighty five thousand Dollars currency
            of the United States of America) on January 1, 2001. Nothing in this
            paragraph shall be construed to constitute Bank's consent to
            Borrower's not paying the Gise Obligations in full on January 1,
            2001, and if not sooner declared due and payable, the Gise
            Obligations shall be due and payable in full on January 1, 2001 as
            provided in Section 2.07 hereof."

         4. REPRESENTATIONS AND WARRANTIES OF LOAN PARTIES. As an inducement to
Bank to enter into this Fifth Amendment, each Loan Party makes the following
representations and warranties to Bank (which survive the execution and delivery
of this Fifth Amendment):

            a. Each Loan Party is in compliance in all material respects with
all covenants contained in the Loan Agreement and the documents related thereto.

            b. All representations and warranties of each Loan Party contained
in the Loan Agreement and the other Gise Loan Documents are true and correct in
all material respects on and as of this date.

            c. No default exists under the Loan Agreement.

            d. No adverse change in condition (financial or otherwise) of
Borrower or any of its Affiliates not previously disclosed to the Bank in
writing or any other event has occurred which creates a possibility of adversely
affecting: (i) the condition (financial or otherwise) of Borrower or any of its
Affiliates, or Borrower and its Affiliates taken as a whole; (ii) the validity
or enforceability of the Loan Agreement or any documents related thereto; or
(iii) the ability of Borrower, or any Affiliate of Borrower, to meet and carry
out their respective obligations under the Loan Agreement or any documents
related thereto or to perform the transactions contemplated thereby.

            e. All information that any Loan Party or any Affiliate of a Loan
Party has provided to Bank in connection herewith is true and accurate and no
Loan Party nor any Affiliate of a Loan Party has failed to disclose any
information of a material nature regarding its financial condition.

            f. Each of the Loan Parties has the full power, authority and legal
right to execute, deliver, perform and observe the provisions of the Loan
Agreement, this Fifth Amendment and any document executed pursuant to this Fifth
Amendment, and to carry out the transactions contemplated hereby and thereby.




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            g. The execution, delivery and performance by each of the Loan
Parties of its respective obligations under the Loan Agreement and the documents
related thereto have been duly authorized by all necessary action, and does not
and will not require any registration with, consent or approval of, or notice
to, or any action by, any person. The Loan Agreement and the documents related
thereto including this Fifth Amendment constitute the legal, valid and binding
obligation of the Loan Parties and each of them enforceable against such party
in accordance with their respective terms.

            h. The execution and delivery of this Fifth Amendment, and the
compliance with its terms as contemplated herein, will not result in a breach of
any of the terms or conditions of, or result in the imposition of any lien,
charge or encumbrance upon any of the collateral referred to in the Loan
Agreement or any document related thereto (the "COLLATERAL") or constitute a
default (with due notice or lapse of time or both) or result in an occurrence of
any event of default for which any holder or holders of indebtedness for
borrowed money may declare the same due and payable under any indenture,
agreement, order, judgment or instrument under which any Loan Party is a party
or by which any Loan Party or the Collateral may be bound or affected, and will
not violate any provision of applicable law.

            i. There are no suits, actions or proceedings (whether or not
purportedly on behalf of Borrower or any Affiliate of Borrower) pending, or to
the knowledge of any Loan Party threatened, against or affecting any Loan Party
or the Collateral at law or in equity, before or by any person which, if
determined adversely to any Loan Party, would have a material adverse effect on
the business or condition (financial or otherwise) of any Loan Party or the
Collateral. No Loan Party is in violation of or in default with respect to any
applicable laws or regulations which materially affect the operations or
conditions (financial or otherwise) of any Loan Party or the Collateral, nor is
it in violation of or in default with respect to any order, writ, injunction,
demand or decree of any court or any person or in violation or in default in any
material respect under any indenture, agreement or instrument, under which any
Loan Party is a party or may be bound, other than as may exist under the Notes.

            j. No property, tangible or intangible, subject to any security
interest, mortgage, deed of trust, pledge, lien, or encumbrance to Bank is
subject to any other security interest, mortgage, deed of trust or encumbrance.

            k. Borrower is a corporation duly organized, validity existing and
in good standing under the laws of Mexico and is authorized to transact business
in all necessary jurisdictions.

         Each Loan Party, jointly and severally, agrees to indemnify and hold
Bank harmless against any losses, claim, damage, liability or expense
(including, without limitation, attorneys' fees) incurred as a result of any
representation or warranty made by it herein proving to be untrue in any
respect.

         5. RATIFICATION OF GUARANTY. Each of ICMOSA and Agromark hereby
recognizes, ratifies, approves and confirms the validity of its respective
Affiliate Guaranty and agrees that said Affiliate Guaranty continues to secure
the indebtedness evidenced by the Loan Agreement as amended by this Fifth
Amendment and the documents related thereto. Group hereby recognizes, ratifies,
approves and confirms the validity of the Group Guaranty and agrees that the
Group Guaranty continues to secure the indebtedness evidenced by the Loan
Agreement as amended by this Fifth Amendment and the documents related thereto.
The Affiliate Guaranties and the Group Guaranty are referred to individually as
a "GUARANTY AGREEMENT" and collectively as the "GUARANTY AGREEMENTS."

         6. REPRESENTATIONS AND WARRANTIES OF GUARANTORS. As an inducement to
Bank to enter into this Fifth Amendment, each of Group and the Guarantors make
the following representations and warranties to Bank (which survive the
execution and delivery of this Fifth Amendment):

            a. No adverse change in condition (financial or otherwise) of Group
or any Guarantor not previously disclosed to Bank in writing or any other event
has occurred which creates the possibility of adversely affecting: (i) the
condition (financial or otherwise) of Group or any Guarantor; (ii) the validity
or enforceability of any Guaranty Agreement; or (iii) the ability of Group or
any Guarantor to meet and carry out its respective obligations under any
Guaranty Agreement.




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<PAGE>   5

            b. Subject to Bank's waiver of the defaults of specific provisions
of the Loan Agreement set forth herein, each of Group and the Guarantors is in
compliance in all material respects with all covenants contained in the Guaranty
Agreements.

            c. All representations and warranties of each of Group and the
Guarantors contained in the Guaranty Agreements are true and correct in all
material respects on and as of this date.

         7. RATIFICATION OF PLEDGE AGREEMENT. Each of Group and Pledgors hereby
recognizes, ratifies, approves and confirms the validity of the Pledge Agreement
and agrees that the Pledge Agreement continues to secure the indebtedness
evidenced by the Loan Agreement as amended by this Fifth Amendment and the
documents related thereto.

         8. REPRESENTATIONS AND WARRANTIES OF PLEDGORS. As an inducement to Bank
to enter into this Fifth Amendment, each of Group and the Pledgors make the
following representations and warranties to Bank (which survive the execution
and delivery of this Fifth Amendment):

            a. No adverse change in condition (financial or otherwise) of Group
or any Pledgor not previously disclosed to Bank in writing or any other event
has occurred which creates the possibility of adversely affecting: (i) the
condition (financial or otherwise) of Group or any Pledgor; (ii) the validity or
enforceability of the Pledge Agreement; or (iii) the ability of Group or any
Pledgor to meet and carry out its respective obligations under the Pledge
Agreement.

            b. Subject to Bank's waiver of the defaults of specific provisions
of the Loan Agreement set forth herein, each of Group and the Pledgors is in
compliance in all material respects with all covenants contained in the Pledge
Agreement.

            c. All representations and warranties of each of Group and the
Pledgors contained in the Pledge Agreement are true and correct in all material
respects on and as of this date.

         9. RATIFICATION OF COLLATERAL ASSIGNMENT. Group hereby recognizes,
ratifies, approves and confirms the validity of the Collateral Assignment and
agrees that the Collateral Assignment continues to secure the indebtedness
evidenced by the Loan Agreement as amended by this Fifth Amendment and the
documents related thereto.

         10. REPRESENTATIONS AND WARRANTIES OF GROUP RELATING TO COLLATERAL
ASSIGNMENT. As an inducement to Bank to enter into this Fifth Amendment, Group
makes the following representations and warranties to Bank (which survive the
execution and delivery of this Fifth Amendment):

            a. No adverse change in condition (financial or otherwise) of Group
not previously disclosed to Bank in writing or any other event has occurred
which creates the possibility of adversely affecting: (i) the condition
(financial or otherwise) of Group; (ii) the validity or enforceability of the
Collateral Assignment; or (iii) the ability of Group to meet and carry out its
obligations under the Collateral Assignment.

            b. Subject to Bank's waiver of the defaults of specific provisions
of the Loan Agreement set forth herein, Group is in compliance in all material
respects with all covenants contained in the Collateral Assignment.

            c. All representations and warranties of Group contained in the
Collateral Assignment are true and correct in all material respects on and as of
this date, except that as of this date the outstanding principal indebtedness
owed to Group under the Collateral Note is $920,430.00.

         11. NO RELEASE OF ANY LOAN PARTY. Nothing herein contained shall
operate to release any Loan Party from liability to keep and perform all of the
terms, conditions, obligations and agreements contained in the Loan Agreement or
any of the other Gise Loan Documents.

         12. NO RELEASE OF GUARANTORS. Nothing herein contained shall operate to
release any of Group or the Guarantors from liability to keep and perform all of
the terms, conditions, obligations and agreements contained in each respective
Guaranty Agreement.




                                     Page 5
<PAGE>   6

         13. NO RELEASE OF PLEDGORS. Nothing herein contained shall operate to
release any of Group or the Pledgors from liability to keep and perform all of
the terms, conditions, obligations and agreements contained in the Pledge
Agreement.

         14. NO RELEASE OF GROUP UNDER COLLATERAL ASSIGNMENT. Nothing herein
contained shall operate to release Group from liability to keep and perform all
of the terms, conditions, obligations and agreements contained in the Collateral
Assignment.

         15. OBLIGATIONS UNAFFECTED. Except as otherwise specified herein, the
terms and provisions hereof shall in no manner impair, limit, restrict, novate
("novacion"), or otherwise affect the obligations of the Loan Parties to Bank as
evidenced by the Loan Agreement and the other Gise Loan Documents. As a material
inducement to Bank to execute and deliver this Fifth Amendment, each of the Loan
Parties acknowledges that there are no claims or offsets against, or defenses or
counterclaims to, the terms or provisions of and the other obligations created
or evidenced by the Loan Agreement or any document related thereto. The parties
agree that this Fifth Amendment does not imply a novation of the original
obligations, and all those provisions and covenants which have not been
expressly amended by this Fifth Amendment will remain in full force and effect,
binding the parties as executed. This Fifth Amendment shall be construed jointly
with the Loan Agreement and the other Gise Loan Documents.

         16. NO WAIVER BY THIS FIFTH AMENDMENT. Each of the parties hereto
acknowledges that, except to the extent expressly set forth herein, the
execution of this Fifth Amendment by Bank is not intended nor shall it be
construed as: (a) an actual or implied waiver of any default under the Loan
Agreement or any document related thereto; or (b) an actual or implied waiver of
any condition or obligation imposed upon any of the parties hereto pursuant to
the Loan Agreement or any document related thereto; (c) an actual or implied
waiver of any condition or obligation imposed upon any of the Loan Parties; or
(d) affecting any right or rights which Bank may now have or may have in the
future under or in connection with the Loan Agreement or any document related
thereto.

         17. CONDITIONS OF EFFECTIVENESS.

             a. Bank shall have received this Fifth Amendment executed by
Borrower, each Guarantor, Group, and each Pledgor.

             b. Corporate resolutions of each of Borrower, each Guarantor, and
Group authorizing the execution, delivery and performance of this Fifth
Amendment and satisfactory to Bank in form and content.

             c. Incumbency Certificate to the satisfaction of Bank from Borrower
containing specimen signatures of all officers of Borrower who are authorized to
execute or attest to this Fifth Amendment or any of the other Gise Loan
Documents on behalf of Borrower executed by the President and by the Secretary
of Borrower; such certification may be conclusively relied upon by Bank until
Bank receives notice in writing from Borrower to the contrary and provides a
substitute certificate conforming to the requirements specified by Bank.

             d. Incumbency Certificate to the satisfaction of Bank from Group
containing specimen signatures of all officers of Group who are authorized to
execute or attest to this Fifth Amendment or any of the other Loan Documents on
behalf of Group executed by the President and by the Secretary of Group; such
certification may be conclusively relied upon by Bank until Bank receives notice
in writing from Group to the contrary and provides a substitute certificate
conforming to the requirements specified by Bank.

             e. Incumbency Certificate to the satisfaction of Bank from ICMOSA
containing specimen signatures of all officers of ICMOSA who are authorized to
execute or attest to this Fifth Amendment or any of the other Loan Documents on
behalf of ICMOSA executed by the President and by the Secretary of ICMOSA; such
certification may be conclusively relied upon by Bank until Bank receives notice
in writing from ICMOSA to the contrary and provides a substitute certificate
conforming to the requirements specified by Bank.




                                     Page 6
<PAGE>   7

             f. Incumbency Certificate to the satisfaction of Bank from Agromark
containing specimen signatures of all officers of Agromark who are authorized to
execute or attest to this Fifth Amendment or any of the other Loan Documents on
behalf of Agromark executed by the President and by the Secretary of Agromark;
such certification may be conclusively relied upon by Bank until Bank receives
notice in writing from Agromark to the contrary and provides a substitute
certificate conforming to the requirements specified by Bank.

             g. All the conditions precedent set forth in Section 3.2,
ADDITIONAL CONDITIONS, of the Loan Agreement shall be satisfied.

             h. Payment of all costs and expenses of Bank (including the
reasonable fees of Bank's counsel) in connection with the preparation of this
Fifth Amendment and any other documents in connection therewith.

             i. Bank shall have received such other documents, opinions,
certifications, consents, waivers, agreements and evidence as Bank may
reasonably request.

         18. EXPENSES, WAIVER FEE AND INDEMNITY. The parties hereto agree,
whether or not the transactions herein contemplated shall become effective, to
reimburse and hold Bank harmless against any liability for the payment of all
out-of-pocket expenses arising in connection with the preparation, delivery,
administration (including, without limitation, any modification of, or consent
or waiver under, the Loan Agreement or any other Gise Loan Document), amendment,
interpretation or enforcement of this Fifth Amendment, including, without
limitation the reasonable fees and expenses of legal counsel for Bank. Further,
each of the Loan Parties jointly and severally agrees to indemnify Bank from and
hold it harmless against any and all losses, liabilities, claims, damages and
expenses incurred by Bank arising out of its entering into any of this Fifth
Amendment, including without limitation, the fees and disbursements of counsel
incurred in connection with any litigation or other proceeding arising out of or
by reason of any of the aforesaid.

         19. CONFIRMATION OF CONTINUED EFFECTIVENESS OF LOAN AGREEMENT. Each
Loan Party hereby confirms and agrees that the Loan Agreement and each of the
documents related thereto secures and shall continue to secure, in the same
manner and to the same extent provided therein, the payment and performance of
the obligations, as extended by this Fifth Amendment.

         20. SEVERABILITY OF PROVISIONS. In case any one or more of the
provisions contained in this Fifth Amendment should be invalid, illegal, or
unenforceable in any respect, the validity, legality, or enforceability of the
remaining provisions contained herein shall not in any way be affected or
impaired thereby.

         21. SUCCESSORS AND ASSIGNS. This Fifth Amendment shall be binding upon
and inure to the benefit of each of the Loan Parties and Bank and their
respective heirs, administrators, successors and assigns; provided, however,
that none of such entities may not transfer its rights under this Fifth
Amendment to any other person without the prior written consent of Bank.

         22. GOVERNING LAW. THIS FIFTH AMENDMENT SHALL BE GOVERNED BY THE LAWS
OF MEXICO WITHOUT GIVING EFFECT TO ANY CONFLICTS OF LAWS PRINCIPLES.

         23. AMENDMENT AND WAIVER. No provision of this Fifth Amendment
(including, without limitation, any of the documents that are attached hereto in
the form of exhibits) may be amended, modified, supplemented, changed, waived,
discharged or terminated unless each party hereto consents in writing.

         24. FURTHER ASSURANCES. Each of the Loan Parties shall from time to
time execute and deliver all such other documents, instruments and assurances
hereof and take all such other actions as may be necessary or reasonably
required by Bank to carry into force and effect the purpose and intent of this
Fifth Amendment.

         25. AGREEMENT CONTROLLING. In the event of a conflict between the terms
and provisions of this Fifth Amendment and the terms and provisions of the Loan
Agreement, the terms and provisions of the Loan Agreement shall control.


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<PAGE>   8


         26. ENTIRE AGREEMENT. This Fifth Amendment (including its recitals and
exhibits) constitutes the entire agreement between the parties with respect to
the subject matter hereof, and this Fifth Amendment (including its recitals and
exhibits) supersedes all previous negotiations, discussions and agreements
between the parties with respect to the waiver of defaults, and no parol
evidence of any prior or other agreement with respect thereto shall be permitted
to contradict or vary the terms hereof.

         27. COUNTERPART EXECUTION. This Fifth Amendment may be executed in any
number of counterparts with the same effect as if all parties hereto had signed
the same document. All such counterparts shall be construed together and shall
constitute one instrument. In making proof hereof it shall only be necessary to
produce one such counterpart.

         28. HEADINGS. The headings of the sections, paragraphs and subdivisions
of this Fifth Amendment are for the convenience of reference only, and are not
to be considered a part hereof and shall not limit or otherwise affect any of
the terms hereof.

         29. NO ORAL AGREEMENTS. THIS FIFTH AMENDMENT REPRESENTS THE FINAL
AGREEMENT BETWEEN THE PARTIES WITH RESPECT TO THE TRANSACTIONS THEREIN DESCRIBED
AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT
ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN
THE PARTIES.

         IN WITNESS WHEREOF, the parties hereto have caused this Fifth Amendment
to be duly executed by their respective duly authorized officers to be effective
as of the 1st day of September 2000.

                          BORROWER:

                          GRUPO INDUSTRIAL SANTA ENGRACIA, S.A. DE C.V., a
                          Mexican corporation


                          By: /s/ Jose Maria Martinez Brohez
                             --------------------------------------------------
                          Name:   Jose Maria Martinez Brohez
                               ------------------------------------------------
                          Title:  President
                                -----------------------------------------------

                          BANK:

                          COOPERATIEVE CENTRALE RAIFFEISEN-BOERENLEENBANK
                          B.A., "RABOBANK INTERNATIONAL," NEW YORK BRANCH,
                          a New York State licensed branch of a Netherlands
                          Cooperative Banking Organization


                          By: /s/ Robert Stevens
                             --------------------------------------------------
                          Name:   Robert Stevens
                               ------------------------------------------------
                          Title:  Vice President
                                -----------------------------------------------

                          By: /s/ W. Jeffrey Vollack
                             --------------------------------------------------
                          Name:   W. Jeffery Vollack
                               ------------------------------------------------
                          Title:  Senior Credit Officer, Senior Vice President
                                -----------------------------------------------




                                     Page 8
<PAGE>   9


                          GUARANTORS:

                          INDUSTRIAS CITRICOLAS DE MONTEMORELOS, S.A. DE C.V.,
                          a Mexican corporation


                          By: /s/ Rafael Vaquero Bazan
                             --------------------------------------------------
                          Name:   Rafael Vaquero Bazan
                               ------------------------------------------------
                          Title:  President
                                -----------------------------------------------


                          AGROMARK S.A. DE C.V., a Mexican corporation


                          By: /s/ Rafael Vaquero Bazan
                             --------------------------------------------------
                          Name:   Rafael Vaquero Bazan
                               ------------------------------------------------
                          Title:  President
                                -----------------------------------------------

                          GROUP:

                          THE UNIMARK GROUP, INC.


                          By: /s/ David E. Ziegler
                              -------------------------------------------------
                          Name:   David E. Ziegler
                               ------------------------------------------------
                          Title:  Chief Financial Officer
                                -----------------------------------------------

                          PLEDGORS:


                          /s/ Rafael Vaquero Bazan
                          -----------------------------------------------------
                          MR. RAFAEL VAQUERO BAZAN


                         /s/ Jose Maria Martinez Brohez
                         ------------------------------------------------------
                         MR. JOSE MARIA MARTINEZ BROHEZ




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